Physics problem....need someone to explain how to do it

A particle moves with velocity v=8t-7, where v is in meters per second and t is in second. (a) find the average acceleration for the one-second intervals beginning at t=3 s and t=4 s. (b) what is the instantaneous velocity and acceleration as functions over time?

A)
(25-17)/1=+8m/sec.sq
B)
v=8t-7
a=8 (because acceleration is derivation of velocity).

a) The acceleration is +8 m/s² at all times

b) Your given equation defines the instantaneous velocity as a function of time. For acceleration, see (a).