i did this in high school and i remember understanding it.. but now i'm really rusty and a bit confused:

in this particular problem set, i am given a graph, and below it,

and i am asked to find the area of the shaded region

i know the formula for area just fine, with the integral and all of that..but i'm confused as to how/why one knows that, for this particular graph,

(or equal to), like, how do you know that those are the endpoints when they are not given? our solutions manual just... says that they are there.

any help is appreciated, thank you!