The correct answer is option (c).
The short-run total cost function can be calculated as the sum of fixed costs and variable costs. In this case, the fixed costs are $4,000, and the variable cost per unit of the variable factor is $4,000.
So, the short-run total cost function (TC) is:
TC = Fixed Costs + (Variable Cost per Unit * Amount of Variable Factor)
TC = $4,000 + ($4,000 * x)
Now, we can use the production function y = 4x^2 to express x in terms of y:
x = sqrt(y/4)
Substitute this expression for x into the total cost function:
TC = $4,000 + ($4,000 * sqrt(y/4))
Simplify further:
TC = $4,000 + ($1,000 * sqrt(y))
So, the correct short-run total cost function is:
TC = $4,000 + $1,000 * sqrt(y)
This matches option (c):
c. 4,000 + 0.25y²