Question

A 100 g piece of aluminum is heated to 90°

Answer 1

When two objects are in contact, it should be that the heat lost is equal to what is gained by the other. From this, we can calculate things. We do as follows:

Heat = mC(Tf-T)
6300 J = (100)(C)(90 - 20)
C = 0.9 J/g °C

Hope this answers the question.