Stuck on this problem, help would be appreciated

The depth of a lake at a certain point, wich is a function of the distance of that point from shore, is 30 feet.

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

Miss henderson wants to build a fence around a rectangular garden in her backyard in the scale drawing the perimeter of the garden is 14 in of the actual length of a b is 20 ft how many feet of fencing what you need