How does the amount of a substance affect the rate
at which temperature changes?

Remember that the slower the temperature changes, the amount of heat is the same. So basically the amount of substance is what determines how much heat there is available for the temperature to change.After that you calculate.

Source:
Yahoo

The more substance you have, the slower the temperature change. 

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.