What scale factor was applied to the first rectangle to get the resulting image? the answer is a decimal. the big rectangle is 2.5 and the smaller one is 0.5

Scale factor is always (new/original)

so it depends which rectangle came first. if it started as large and was dilated to the smaller one, then the ratio is (.5/2.5) which simplifies to 1/5 or 0.2.

B. 2 1/2 feet. multiply 2.5 inches by 12 to get thirty inches then divide by 12 to get 2.5 feet