The following information are given in the question:
Mass, M = 8 g
Temperature, T = 20 degree Celsius
Specific heat of water [this value is a constant] C = 1 c/gc
Heat, Q = ?
The formula for calculating the amount of heat required is given below:
Q = MCT = 8 * 1 * 20 = 160
Therefore, Q = 160 cal.