Answer:
x=11 (read below)
Step-by-step explanation:
7 + x = 18
Subtract 7 from both sides
x=11
It's quite simple because if you do something to one side of the equation, you need to do it to the other because otherwise the equation won't be equal. This is how you need to simplify most problems, by taking something from one side and taking from the other as well.
