Verified Answer :

1 foot = 12 inches, but
Scale
= 2.5 inches : 20 feet
= 1 inch : 8 feet

New size = 28 feet
Therefore,
Let the corresponding measurement be x inches.
So,
1 : 8 = x : 28
1 x
-- = ----
8 28

28
x = ---- = 3.5 inches
8

Kunchan

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