I've been having a hard time with this graph problem. Go to this link and scroll down to #3 -

http://www.collegeboard.com/prod_dow..._bc_frq_01.pdf
(a.) Hm. I'm going to say that the velocity is increasing at t=2 because the acceleration graph basically traces the value of the slope of v(t). The graph is positive (and thus velocity increases) at t=2. Am I right?

correct ... v(t) and a(t) are both > 0
(b.) Maybe t=12? It looks like, at t=12, there's net acceleration of zero...?

correct, because $\displaystyle \textcolor{red}{55 + \int_0^{12} a(t) \, dt = 0}$

(c.) I'm pretty sure it's t=6 because it satisfies the first derivative test.

yes, absolute max velocity = $\displaystyle \textcolor{red}{55 + \int_0^6 a(t) \, dt}$

(d.) I don't think there's any time. Just my hunch. Probably because there's not enough negative element in a definite integral of a(t) to cancel the initial velocity or something, I don't know.

absolute min velocity = $\displaystyle \textcolor{red}{55 + \int_0^{16} a(t) \, dt > 0}$