Philip P. answered • 04/15/14

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Let n = the unknown number

*Three times the sum of a number (n) and 7 is 45*

The sum of the number (n) and 7: n+7

Three times the sum of the number and 7: 3(n+7)

Three times the sum of a number and 7 is 45: 3(n+7)=45

Distribute the 3 across the terms in the parentheses:

3(n + 7) = 45

3n + 21 = 45

Solve for n