Please help me solve four caculus problems, I need detailed process. And take photo of the process, thanks.

8. At a baseball stadium, souvenir hats are sold at two locations. If r, and 2 are the numbers of baseball hats sold at Location 1 and Location 2, respectively, then the total revenue for the hats is modeled by R = 15x1 + 16x2 - E 12 100 When m = 50 and 12 = 40, find (a) the marginal revenue for location 1, (b) the marginal revenue for location 2