Need help with this one please explain how you got it

Answer:
B) 40 feet
Step-by-step explanation:
Essentially, there are two similar right triangles in the given problem.
base_L = Base [larger triangle] = 60 ft
base_S = Base [smaller triangle] = 6 ft
x = leg (larger triangle)
y = leg (smaller triangle) = 4 ft
Using the given proportion to solve for the value of x:
[tex]\frac{x}{base_{_L} } = \frac{y}{base_{_S} }[/tex]
[tex]\frac{x}{60ft} = \frac{4 ft}{6 ft}[/tex]
6x = 240
Divide both sides by 6:
6x/6 = 240/6
x = 40