Posted by Kyle on .
The position s of a point (in feet) is given as a function of time t (in seconds).
s = −10 + t − 15t2; t = 8
(a) Find the point's acceleration as a function of t.
s''(t)=
I know this answer, it is 30
(b) Find the point's acceleration at the specified time.
s''(8) = I don't know this one

Brief Calculus 
Reiny,
s = 10 + t  15t^2
s' = v = 1  30t
s'' = a = 30 , which is a constant
so no matter what value of t you take, e.g. t = 30
there is no variable to sub into, so
a = 30