The first step is to find the scale factor relating ABC to A'B'C'. Since they are dilated, ABC is similar to A'B'C'. This means that the ratios of their corresponding sides are equal. Thus,
AB/A'B' = BC/B'C' = AC/A'C'
From the information given,
AB = 7
A'B' = 28
Thus,
ratio of ABC to A'B'C' = 7/28 = 1/4
Ratio of area of ABC to A'B'C' = (1/4)^2
Ratio of area of ABC to A'B'C' = 1/16