Question

Assume that each of the follwing functions gives the position of an object at time t. Find the velocities indicated by setting up and evaluating a limt algebraically.

(a) s(t) = 3t^2, Find v(-1).
(b) s(t) = 1/t , Find v(2).
(c) s(t) = square root of t, Find v(1).

The answers that I got were the following...
a)3
b)1/2
c)1

I did them another way and the answers I got were
a)-6
b) -(1/4)
c) I didn't really get any answers here.

Please tell me which answers are right or if any of them are right...