The marginal cost is $MC = 4x + 5$ rupees. By how much does the total cost rise when output goes up from 20 to 30 units?

Explanation

1. 01

   The rise is $\int_{20}^{30} (4x + 5)\,dx = \left[2x^{2} + 5x\right]_{20}^{30}$.

2. 02

   $= (1{,}800 + 150) - (800 + 100) = 1{,}050$ rupees. The fixed cost cancels out.