Answer: 48
Step-by-step explanation:
Firstly, we need to solve the marginal product which will be:
= dM/dx
= d(100x - x²)/dx
= 100-2x
At socially optimal level, it should be noted that:
Price × Marginal Product = Cost
90 × (100-2x) = 400
9000 - 1800x = 400
1800x = 9000 - 400
1800x = 8600
x = 8600/180
x = 47.77
x = 48
Therefore, the optimal number of workers will be 48.