The cost of manufacturingxcases of umbrellas isCdollars (in thousands), where

Monthly production attweeks is expected to be

I know that = 18(5000+80t)+4sqrt(5000+80t)+9

and that marginal cost or = 28+(2/x^.5)

I'm not sure how to find in order to solve the equation for t=2 in order to find how fast costs are rising per week.