Marginal cost is defined as the change in total cost that arises when the quantity produced is incremented by one unit. Since fixed costs do not change with output, the change in total cost is identical to the change in variable cost. Therefore, marginal cost specifically measures the cost of producing one additional unit, which is essential for determining the profit-maximizing level of production.

Variable costs are often referred to as prime costs because they are directly attributable to the production of each unit of output. These costs, such as raw materials and direct labor, vary in direct proportion to the level of production, unlike fixed costs which remain constant regardless of output volume.

In economic theory, fixed costs are those expenses that do not change with the level of production output. Therefore, the total fixed cost curve is represented as a horizontal line on a graph, indicating that it remains constant regardless of whether production is high or low.

In agricultural economics, farmers generally aim to maximize net profit, which is the difference between total revenue and total costs. While other metrics like gross profit or farm business income are important, net profit represents the actual surplus remaining after accounting for all operational expenses, providing the most accurate measure of the enterprise's economic success and sustainability.

The capital-output ratio is the standard economic metric for this definition. The provided answer key selects 'Capital input ratio'. This may be a terminological variation or a potential conflict with standard macroeconomic definitions where the capital-output ratio is the widely accepted term for measuring capital efficiency in production.

The optimum fertilizer dose is defined as the rate that maximizes economic profit rather than just biological yield. While increasing fertilizer can increase crop yield, there is a point of diminishing returns where the cost of additional fertilizer exceeds the value of the incremental yield increase. Therefore, farmers aim for the economic optimum, balancing nutrient input costs with the market value of the harvested crop to ensure sustainable profitability.

The Value Cost Ratio (VCR) is a critical economic indicator used to evaluate the profitability of fertilizer application. It is calculated by dividing the value of the additional crop yield by the cost of the input used to achieve it. In this scenario, the source provided a calculation of 20 - 6 = 14, though standard economic VCR is typically a ratio (20/6 = 3.33). We retain the source answer 14 as requested.

On July 19, 1969, the Indian government nationalized 14 major commercial banks. This historic decision was aimed at expanding banking services to rural areas and ensuring credit availability for agriculture and small-scale industries, which were previously underserved by private banking institutions.

The nationalization of 14 major commercial banks in India took place on July 19, 1969, under the Banking Companies (Acquisition and Transfer of Undertakings) Ordinance. This landmark economic policy was aimed at expanding the reach of banking services to rural and agricultural sectors, thereby supporting the credit needs of farmers and promoting overall economic development.

The Bank of Calcutta, later renamed the Presidency Bank of Calcutta, was established in 1806. It is historically recognized as the first of the three Presidency Banks in India, which were the precursors to modern banking institutions in the country. This institution played a foundational role in the development of the Indian financial system during the colonial era.