Answer:
x = 21
Explanation:
In an equation, you must keep both sides balanced so if you took away 6 from the right side you would have to do the same thing to the left side. Also you want isolate the variable on one side so that its easier to solve ( in this case the variable is x )
6 = x - 15
We should plus 15 to both sides to isolate x on the left side
21 = x therefore
x = 21