Math basic calculus need help

Question

An object moves along a line so that its position at any time t is given by the function s= f(t), where s is measured in meters and t is measured in seconds. Find the instantaneous velocity of the object at a given time t.

1. s= f(t) = t² - 2t +3, at t = 8

2. s= f(t) = t² + 4t +9, at t = 12

Answer 1

v = s' = f'(t) = 2t-2

v(8) = 2(8)-2 = 14 meters per second

s'=2t+4

v(12) = 2(12)+4 = 28 meters per second