Final answer:
The amount of labor input at which the firm's average and marginal product of labor are equal is 200.
Step-by-step explanation:
To find the amount of labor input at which the firm's average and marginal product of labor are equal, we need to set the average product of labor (APL) equal to the marginal product of labor (MPL).
Mathematically, APL is calculated as Q/L and MPL is the derivative of the production function, which is 3L^2-400L+10,000.
Setting APL = MPL, we get (L^3-200L^2+10,000L) / L = 3L^2-400L+10,000.
Simplifying the equation and solving for L, we find that at L = 200, the average and marginal product of labor are equal.
This confirms the relationship discussed in the text, where the average and marginal product curves intersect.