Use the law of conservation of energy and assuming no heat loss to the surroundings, then
Heat given up by copper = heat absorbed by water + heat absorbed by calorimeter
Working formula is
Q = heat = MCp(delta T)
where
M = mass of the substance
Cp = specific heat of the substance
delta T = change in temperature
Heat given up by copper = 0.10(387)(95 - T)
Heat absorbed by water = 0.20(4186)(T - 15)
Heat absorbed by calorimeter = 0.28(899)(T - 15) \
where
T = final temperature of the system
Substituting appropriate values,
0.10(387)(95 - T) = 0.20(4186)(T - 15) + 0.28(899)(T - 15)
38.7(95 - T) = 1088.92(T - 15)
3676.50 - 38.7T = 1088.92T - 16333.8
1127.62T = 20010.3
T = 17.75 C
