Question

If 3x+9=(10+x) then what does x equal?

Answer 1

Remember you can do anything to an equation as long as you do it to both sides

3x+9=10+x
minus x both sides
3x-x+9=10+x-x
2x+9=10+0
2x+9=10
minus 9 both sides
2x+9-9=10-9
2x+0=1
2x=1
divide both sides by 2
x=1/2

Answer 2

3x + 9 = 10 + x
2x +9 = 10
2x = 1
x = 1/2