The sum of 18 + 45 is a multiple of which sum?

First add 18 + 45 to get 63. The sum in choice B is 2 + 5 = 7, and 63 ÷ 7 = 9, so 63 is a multiple of 7. The other sums, 12, 4, and 18, do not divide 63 evenly.

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