The answer is 767.448 Joules.
Q (Joules of heat) is what you’re solving for.
Q = ?
M (mass) = 2.55g
C (specific heat of water) = 4.18 J/g°C
T (change in temperature) = 100°C - 28°C
(subtracting the initial temp. from the final temp.) = 72°C
Using the equation Q=MCT
Q = (2.55g) (4.18J/g°C) (72°C)
Units for both grams and degrees celsius cancel out, leaving you with joules.
Multiply the numbers to get 767.448 Joules.