You can simplify expressions by combining like terms. Like terms are terms that have the same variable(s) or lack of variables and are to the same power.
If a term doesn't have an exponent, then an exponent of 1 is implied.
The only like terms in the expression (m + 11) + (n + 44) are 11 and 44.
Because they both have no variables and are to the same power.
(m + 11) + (n + 44)
m + 11 + n + 44
m + n + 55
So, m + n + 55 is the simplified form.