Even though I am not CPhill, I can answer. :)
Step 1: Subtract 60 from both sides.
360 = 3x + 60
- 60 -60
Step 2: Divide both sides by 3.
300 = 3x
___ __
3 3
Step 3: Your answer is 100.
x = 100
You can also substitute the x to check your answer. Hope this helps!