First factor the equation
(x-10)(x+2) = 0
Then solve for (x-10) and (x+2)
x=10
x=-2
Marginal profit, P(x) = R(x) - C(x)
P(x) = x³ - 5x² + 7x + 10
x³ - 5x² + 7x + 10 = 0
If you solve it, you get x = -0.839 where P(x) is zero
That would be written as:

And the step-by-step equation would be:
→ we take the 2 to the right side of the equation and do the IO*
→we solve for 
→ final answer
*Ps - IO is not an existing term and stands for inverse operation. In this case, because when we take to 2 to the right side of the equation (the 2 is a power) it'll have to turn into a square root (because exponents and roots are inverse operations)
Hope it helped,
BioTeacher101
D: We solve this in exactly the same way in which we solved the previous area problem. Side length is s, area is s^2. Here, side length is 5 in; area is 25 in^2.
the problem does say, however, not to include units in your answer. Thus, just write "25."