(3m+13)+(4m+21) simplified

(7m+34)

Step-by-step explanation:

Add like terms 3m+4m=7m, 13+21=34

You have to make sure to add like terms.  In algebra, like terms are terms that have the same variables and powers. The coefficients do not need to match. Unlike terms are two or more terms that are not like terms, i.e. they do not have the same variables or powers. The order of the variables does not matter unless there is a power.