Answer:
Yes, it is proportional.
Proportions Explained:
Draw 2 triangles, triangle ABC and triangle DEF. Label any 2 sides of triangle ABC as measuring 18" and 4". Label the 2 corresponding sides of triangle DEF as measuring 72" and 16".
When you see if 18/72 and 4/16 are proportional, you are seeing if triangle ABC and triangle DEF are similar. One way to do it is with proportions, which is the way we are doing it. When making proportions, you want to put corresponding sides into the same fraction. For example, let's say you labeled side AB as 18" and side BC as 4". In triangle DEF, let's say you labeled side DE as 72" and side EF as 16". When making proportions, you want to put the corresponding side lengths (AB and DE) into the same fraction. Second fraction, same way. Just remember that the second fraction has to correspond with the first fraction. If you put the side length of triangle ABC on top and the side length of triangle DEF on bottom, you need to do the same for the second fraction.
But, they did the previous steps and want you to do the rest:
Now you have two fractions: AB/DE and BC/EF, or 18/72 and 4/16. Fully reduce each fraction, and if they come out to the same fully reduced fraction, they are proportional and the two triangles are similar. 18/72 reduces to 1/4 and 4/16 reduced to 1/4. 1/4=1/4, so the final answer is yes.
