From the statement of the question we know that:
• the high temperature was: Th = -3 °F,
,
• and the low temperature was: Tl = -7 °F.
The question asks about the difference between the high (Th) and the low temperature (Tl) for the day, i.e. we must compute the difference:
Replacing the values of the statement, and computing we find that the difference is: