I already answered this question, if you look back in your questions you should find this answered along with another one. I'll do it again just in case you don't find it.
Answer:
{y,x} = {-4,-2}
Expanation:
Solve by Substitution :
// Solve equation [1] for the variable y
[1] y = 2x
// Plug this in for variable y in equation [2]
[2] -2•(2x) - 8x = 24
[2] - 12x = 24
// Solve equation [2] for the variable x
[2] 12x = - 24
[2] x = - 2
// By now we know this much :
y = 2x
x = -2
// Use the x value to solve for y
y = 2(-2) = -4