Answer:
-S = 15
Step-by-step explanation:
You are asked to find the opposite of the given value.
Opposite
The opposite of an integer value is obtained by changing its sign.
S = -15
-S = -(-15) = 15
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Additional comment
Equivalently, you are multiplying by -1. The product of an even number of minus signs is a plus sign. We usually don't write the plus sign for a numerical value.
