How do i solve this problem to find x?

X would have to be a negative because the end result is - 18. We know 5 + 4 = 9 so the negative would have to be - 27 because 9 + 27 = -18 so the answer to your problem is -27. :) Have good day

In order to find x, you need to isolate it, which means to get it by itself on one side of the equation. 
Step 1. Distribute the 3 to the 4 and 5x inside the parentheses. Now your equation looks like 12+15x=-18
Step 2. Now that you have the equation, you need to do the inverse (opposite) operation of whatever is on the left side. In this case, you would be doing subtraction. So you subtract whatever doesn't have the variable in it, so in this case, 12. You subtract 12 from 12 on the left side, and 12 from -18 on the right side. 12-12 cancels out, so the 12 is gone. You finish and get 15x=-30
Step 3. You do the same as step 2, but with division this time as the inverse operation this time. You divide by 15 on both sides, again, with 15 canceling out. You have now, x=-2.
Have a great day!