Need Help Writing Math Problem As Expression

Hello, I need help with the following math problem. It needs to be written as an expression.

Problem: An experiment is underway to test the effect of extreme temperatures on a newly developed liquid. Two hours into the experiment the temperature of the liquid is measured to be -17 degrees celsius. After eight hours of the experiment, the temp. of the liquid is -47 degrees celsius. Assume that the temperature has been changing at a constant rate throughout the experiment and will continue to do so.

Any help with this problem will be greatly appreciated.

Thanks!

David