Answer:
3(b + f)
Explanation:
Through the context of the question, we can determine that both the variables of b and f must be added together, hinted by the word "sum" within the question. The number 3 comes into play when it says "3 times the sum of". Within this context, the number 3 must be multiplied by the sum of both b and f, causing 3 to be placed outside a pair of parenthesis that separates the addition from the multiplication. The reason that the parenthesis is needed is because the question says "3 times the sum of b AND f" (notice is says both b AND f). b and f must go together in order to make this true, so that is why it is placed inside a parenthesis (so that both variables can be multiplied by 3).
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