Given,
initial temperature t1 = 5°C
mass of water m = 20 kg
final temp = 35°C
specific heat capacity of water = 4200 J/ kg°C
heat supplied Q = ??
According to the formula
Q = msdt
Q = 20 * 4200 * 30
Q = 252000 J
Hence heat required to heat 20 kg of water to 35°C is 2.52 * 106 J