How fast was the level of sales increasing at the beginning

Question

The annual sales of digital signal processors (DSPs) in billions of dollars is approximated by

S(t) = 0.14t² + 0.68t + 3.1 (0 ≤ t ≤ 6)

where t is measured in years, with t = 0 corresponding to the beginning of 1997.

a. What were the sales of DSPs at the beginning of 1997? What were the sales at the beginning of 2002?

b. How fast was the level of sales increasing at the beginning of 1997? How fast were sales increasing at the beginning of 2002?