Answer :

First distribute the 3 into the parentheses

You now have 3x+9=15+2x

Then you have to add/subtract like terms.

3x-2x+9=15+2x-2x

x+9-9=15-9

x=6

Hope this helps!
jamilashah
3(x+3)=15+2x      Distribute 
3x + 9=15+2x      subtract 9 from both sides 
3x=6 + 2x            Subtract 2x from both sides 
x=6