Answer: 21a+17b
Step-by-step explanation: To get rid of the parenthese you must multiply or distribute 9 to all the numbers inside the parentheses.
9(a +b) + 4(3a + 2b)
9a+9b+12a+8b
Combine like terms
9a+9b+12a+8b
21a+17b
And we have our answer.
21a+17b Hope this helps!