X+7y=24

X-9y=-24

Work needed for substitution method!

You can use a simultaneous equation - x + 7y=24 minus x-9y = - 24 you end up with 16y = 48

Divide 48 by 16 and you get 3 is equal to y. Now put three into an equation eg, x + 21 = 24 it is now obvious that x = 3 as well as y = 3