The temperature sequence start with the value: 43 degrees F. Next day there is an increase of 6 degrees F, so that takes us to 49 degrees F. the following day there is a decrease of 13 degreef F, which takes us to 36 degrees F
So in order to calculate the change in temperature we do:
Final Temp - Initial Temp = 36 F - 43 F = - 7 F
the overal change in temperature is - 7 F