Math Help - find temp

A pan of water (46 degrees) was put into a fridge. Ten min. later, the temp was 39; 10 min. later, the temp was 33.
Use newtons law of cooling to find the temp of the fridge..
I know the equation.

Do I need to find the rate, or how do I do this?

By Newton's law of cooling you have that the temperature of the water is given by:

where is the temperature of the fridge and r is some unknown rate constant. You are told T(10) = 39 and T(20) = 33, so:


The first equation gives you:

and the second gives you:
.
Equating these two expressions for r and multiplying by -20 yields:
.
The 2 can move inside the log as a power, then you can get rid of the logs and solve. You should get .