Step-by-step explanation:
-7.9(15 +8) . . . . given
-7.9·15 -7.9·8 . . . . . distributive property
-118.5 -63.2 . . . . . . multiplication
-181.7 . . . . . . . . . . . . addition
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The distributive property multiplies terms inside parentheses by the factor outside parentheses. Each term is multiplied by that outside factor. Once that multiplication is shown, it can then be executed and the results summed in accordance with the steps provided.
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Here, it might be simpler to do the addition first, then the multiplication. That is not what this problem is asking you to do.