As you can see, the denominator of 1/3 is 3. 1 third of a is -5. So what you do is, you multiply -5 * 3 and that'll give you -15. So, it is equal to -15.
At the start the temperature is -7 overnight it gets 12 degrees warmer so -7+12 =5 degrees than during the day it gets 12 degrees warmer so 5+12= 17 degrees
