
Marginal Profit
The marginal profit at x is defined as the instantaneous rate of change of profit with respect to the number x of items produced.
Suppose that the total profit in hundreds of dollars from selling x items is given by P(x)=4x^24x+1
The marginal profit when x=4 units are sold equals______ dollars/(unit of production).
I have attempted this question by taking the derivative of P(x)=4x^24x+1 which becomes P'(x)=8x4 and plugged the x=4 into the derivative and got 28; however that is not the correct answer.
Can someone help me please.

looks fine to me, except that you are told to give the answer in $/unit, but your profit function was in 100's of dollars per unit.
answer = 2800