need help in the following

QUESTION 5 A spherical balloon is being inflated and its volume is changing at the rate of 800m' /min. When the radius is 10m, find the rate at which the Area is increasing. V = A = 4x7- (7 marks)QUESTION 7 The number of cars passing a motorway at any time f hours is given by the equation N = - 1 - 61 + 980 Find the time at which maximum number of cars passes the motorway and hence find the number of cars passing at that time. (7marks)