I need help with proportions?

Question

I have no idea how to solve proportional reasoning problems. One of the problems for my homework is to identify whether a constant multiplier or constant ration is used to solve problem. I don't even know what these are!! Haha. Here is an example:

An aerial photograph has a scale of 3 inches equals 20 miles. If the photograph is 12 inches by 18 inches,how many square miles are represented? Create an equation/expression that relates these quantities and identify the representation as a CONSTANT MULTIPLIER or a CONSTANT RATIO.

Please help me!

Answer 1

12/3 = 4

18/3 = 6

There are  FOUR - 3 inches. in 12inches and SIX - 3 inches . in 18 inches

Multiply the FOUR and SIX  with 20

(4)(20) = 80 miles

(6)(20) = 120 miles

THEREFORE:

12 inches = 80 miles

18 inches = 120 miles