According to the data,
20 foot = 2.5 inches
if we want to find out the measurement for 1 foot, 2.5 inches has to be divided by 20.
1 foot = 2.5/20 = 0.125
If it is increased to 28 foot, answer should be multiplied by 28.
0.125*28 = 3.5 in
Answer c is correct