The key to this is understanding that as you integrate velocity with respect to time, you obtain a change in displacement. If you haven't taken calculus, don't worry - basically what I'm saying is that when you take the area under the graph of velocity vs. time, you obtain a net change in displacement.
Take part a for example. The area under the graph is a triangle, whose area is 1/2 * base * height or 1/2 * 2* 9 = 9. Thus the net change in displacement is +9. And since x= x0 + vt, then x = 10 + 9 (the net change in displacement you found from the graph, which is much like velocity times time). Thus, you should obtain an answer of x = 19 at t = 2.
Do the same for the other two parts. For part c, be careful - since the graph goes under the x-axis at time 6, just take the area between the graph and the x-axis as the area under the graph.
Was that clear? Sorry if it wasn't.
Thanks! I got the first two parts down but I still don't understand the third ..
Can someone help clarify how you do the third part?