Problems to go over

ch. 10 problem 9:
The last part on the table, "Time to reach 25 C" is completely off from what I got by integrating the specified equation (10.10) and calculating the value. Everything up to there looks good.

ch. 12 problem 7:
The value of Z_f is very off from what I got, and stuck here.

ch. 9 problems 6, 7:
Very complicated.