I need help with these homework questions

1. An object dropped from the rest from the top of a tall building on Plant x falls a distance s(t)=14t^2 feet in the first t seconds. Find the average spped of the object during the frist 9 seconds of fall.

2. often sales of a new product grow rapidly at frist and then level off with time. This is the case with the sales reprensented by the function S(t)=400-100t^-1, where t represents time in years. Find the rate of change of sales for the following number of years.

a. 4 years.

b. 9 years.

3. Consider the function f(x)=x^2 -3x -5

a. find f(a+h)

b. find f(a+h)-f(a)/h

c. Find the instantaneous rate of change of f when a=4.