Find velocity of the object after t seconds

Question

An object with an initial velocity of  m/s undergoes an acceleration of  ,  seconds after an experiment begins.The velocity of the object after  seconds is $\mathrm{v(t)=}$

Answer 1

a(t) = v'(t)

So, v'(t) = -6t - 18 and v(0) = 5

v(t) = ∫v'(t)dt = -3t² - 18t + C

Since v(0) = 5, v(t) = -3t² - 18t + 5