It's 17.
Here's Why:
Since it's asking, "What is the approximate height of the tree after 10 years?" 10 is the main clue/hint because at the bottom of the graph,it says, "time (yr)." So, you start from the bottom but line up with the #10, then work your way up and you have to stop at the line & then you look to the side of the graph (left side), where it says, "height" & it'll be 17. As a point, it is (10, 17) where 10 is time(x) & 17 is height(y).
Hope this helps you!!! :)