The sum of the polynomials (m + n + 3) + (m + n + 4) is 2m + 2n + 7.
The sum of the polynomials (m + n + 3) + (m + n + 4) can be found by combining like terms.
First, we can group the like terms together. The terms with "m" and "n" can be combined, as well as the constant terms 3 and 4.
So, combining the "m" terms, we have m + m, which is equal to 2m.
Similarly, combining the "n" terms, we have n + n, which is equal to 2n.
Lastly, combining the constant terms, we have 3 + 4, which is equal to 7.
Putting it all together, the sum of the polynomials (m + n + 3) + (m + n + 4) is equal to 2m + 2n + 7.
Therefore, the final answer is 2m + 2n + 7.