
Christopher G. answered 07/21/13
Math Tutor - Algebra, Trig, Calculus, SAT/ACT Math
To solve this equation, we need to get y alone on one side of the equal sign. To do this, we need to move the - 9 over to the left side. This means adding 9 to both sides of the equation.
11 = y - 9
+ 9 + 9
20 = y - 9 + 9
The - 9 and + 9 cancel out to 0, so we get 20 = y.
To check, we can always plug the value we get for the variable into the original equation.
11 = y - 9 -> 11 = 20 - 9 -> 11 = 11 It checks out!