Amt. of heat absorbed by the body E= mc T
= m x 0.2 x 100 x 100 = 100 m kcal

Gain in mass = m = E/c^2
=(20m x 4.2 x 10^3)/(3 x 10^8)^2

So, percentage increase in mass = m/m x 100%

=(20m x 4.2 x 10^3) x 100 %/(3 x 10^8)^2 x m
= 9.3 x 10^ -11 %

So percentage increase in mass is 9.3 x 10^ -11 %.