This is what I have so far:Let's assume we find a dead body in a room with a constant temperature of 24 degrees.

At 8a.m, the body has a temperature of 28 degrees. At 9a.m it has a temperature of 26 degrees. Assuming normal body temperature is 37 degrees, when was the person killed?

I need to find k.

Both these equations give:

Hence:

However, my book says k should be . What's going wrong?