Given the average cost function
AC =2Q-5 +7Q Find an expression for marginal cost. If current output is 20 units. Compute the effect on total cost of an increase in production of 15units.
marginal cost is the derivative of the average cost, right? So,
2Q-5 + 7Q is useless, so I assume it is
2Q^.5 + 7Q
if so, then MC = 1/√Q + 7
Now see what you can do with that.