I will assume the question is about #20 as it is the only unanswered question. In order to find the ratio you must find the surface area of both boxes. Find the surface area of one side of each box, and write the ratio:
12 x 12 = 144
18 x 18 = 324
The ratio is 144 : 324
Reducing we get 35 : 81
We can also write a ratio as a fraction 35 / 81. The reason we do not to find the surface area of the whole box is because we are going to reduce it anyway and it will still become 35 : 81.
