Maybe i have that you wanted
We can represent the situation like that:
Y=-15 and x=-20
Then When y=12 x=?
We make x(The unknown) *-15=12*(-20)
We have an simple équation to solve
Thus x=(12*(-20))/-15
X=16
Your proof is correct and very well done
<span>8x(6 + 7y) this is your answer hope it works!</span>
