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 expressions by combining like terms: (m + n + 3) + (m + n + 4) = m + m + n + n + 3 + 4 = 2m + 2n + 7. The sum is 2m plus 2n plus 7, choice C.

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