Understand the example but not this question, other than by common sense.

Question

A scale drawing of an office building is not labeled, but indicates 1/4 inch = 5 feet. On the drawing, one wall measures 2 inches. How long is the actual wall?

Answer 1

1/4 inch=5 feet

how many 1/4 inches are in 2 inches ?

2/(1/4)=8 and each one represents 5 feet; therefore 8*5=40 feet

also, you can set up a proportion...

(1/4)/5=2/n

cross multiply

(1/4)n=5*2, (1/4)n=10, n=4*10, n=40 again