There is a given point (10,3) this shows that when the width (X) is 10, the height (Y) is 3.
On the left side of the graph, they show an equation for the height Hw as being the constant over w ( width).
Using the given point solve for the constant.
Replace Hw with 3 and w with 10:
3 = Constant/10
Solve for the constant by multiplying both sides by 10:
Constant = 3 x 10
Constant = 30
The answer is B.