R(x)=400x-20x^2 find the maximum

What is the radius of a circle with an area of 78.5 cubic inches? use 3.14 for pie

Meghan has created a diagram of her city with her house, school, store, and gym identified. a. how far is it from the gym to the store? b. meghan also wants to walk to get some exercise, rather than going to the gym. she decides to walk along arc ab. how far will she walk? round to 3 decimal places.

Me get the answer and explain to me the steps to solve it would be greatly appreciated : )