Once you attempt the question then PrepInsta explanation will be displayed.
Let MP = X and CP = 100
Now,
X - 16% of X = 100 + 20% of 100
X - 0.16X = 120
0.84X = 120
X = 143 (Aprox.)
Now, discount is 20% then,
SP = 143 - 20% of 143 = 114. 42
Gain = 14.42
% gain = (14.42 * 100)/100 = 14.42 = 14 (3/7).