Answer
$|t-325| \leq 7$, or (D)
Work Step by Step
If the temperature varies between +7 and -7 of the setting, this means two things. First of all, the wording implies that this includes +7 and -7. This also means that the difference cannot be more than +7 or -7.
In other words, the absolute value of the difference cannot be more than 7.
$|difference| \leq 7$. Difference would be $|Temp - set point| = |t-325|$
So, the answer is $|t-325| \leq 7$, or (D)
