Final answer:
The marginal cost when x=25 is 2 dollars.
Step-by-step explanation:
To find the marginal cost, we need to find the derivative of the cost function with respect to x. Let's start by rewriting the cost function C = 20√x - 625 + 705. Taking the derivative with respect to x, we get C' = 10/√x. Now we can plug in x = 25 to find the marginal cost: C' = 10/√25 = 10/5 = 2. Therefore, the marginal cost C' when x=25 is 2 dollars.