The bold line goes from 10 to 50.
So you know that the minimum height is 10 and the maximum height is 50.
Also, it is continuos, because all the segment, from 10 to 50 is in bold.
Also, you know that the extreme points (10 and 50) are included, because the circles of the points are filled.
So, given that h represents the height, the answer is 10 ≤ h ≤ 50 (option B).