Which equation results from adding the equations in this system?

x + 6 y = 9. Negative x + 2 y = negative 15.
8 y = negative 6
8 y = 6
4 y = 24
4 y = negative 6

Atheater wants to build movable steps that they can use to go on and off the stage. they want the steps to have enough space inside so they can also be used to store props. how much space is inside the steps?