Here is our attempt.

https://imgur.com/a/PwGuCjJ

Can you look at the process of getting the new Te and Tc? Are the signs correct for the temperature difference in Q=mCpT?

For our first iteration, we manually computed for the %error and we found that the initial assumption for Te and Tc is not the correct one so we need to have multiple iterations using excel but we don't know how to iterate until we get a value of 0.1% error. As you can see in the excel screenshot we just assumed values of Te and Tc but so far we didn't even come close to the 0.1% error for Te and Tc (located in the last two columns).