$100
100% would be doubling it.
Answer: 15, because it is 16-1
Could you possibly put it in a picture?

For each subset it can either contain or not contain an element. For each element, there are 2 possibilities. Multiplying these together we get 27 or 128 subsets. For generalisation the total number of subsets of a set containing n elements is 2 to the power n.
Answer:
7.5in explanation:4in+2in+1.5in=7.5in