Hey there! :)
3ab + 4ab + 5
In order to simplify this, we must add like terms. In addition, when simplifying, you can ONLY add like terms.
Since both "3ab" & "4ab" contain "ab," you are able to combine them together!
When combining like terms, you only add the numerical value, not the letters.
This leaves us with : 7ab + 5
Therefore, your answer is 7ab + 5
~Hope I helped!~