Help me please I don’t understand it

Mat bought a phone for $100. he has to pay $30 per mouth. if he has paid $640 in total, how many mouth has he had the phone?

The function v(r)=4/3pir^3 can be used to find the volume of air inside a basketball given its radius. what does v(r) represent

Find the center of the circle that can be circumscribed about efg with e(4,4) f(4,2) g(8,2)