What is the sum of the polynomials? open paren m plus n plus 3 close paren plus open paren m plus n plus 4 close paren

Add the like terms in (m + n + 3) + (m + n + 4): m + m = 2m, n + n = 2n, and 3 + 4 = 7. The sum is 2m + 2n + 7, which is choice D.

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