By substituting x = -9 into the equation 8x - 9y = -18 and solving for y, we find that the final answer is x = -9, y = -6.
To solve the system of equations using substitution, we have been given that x = -9. The second equation provided is 8x - 9y = -18. To begin, we substitute x = -9 into the second equation, which then becomes 8(-9) - 9y = -18. Performing the multiplication, we get -72 - 9y = -18. To find the value of y, we solve for y by adding 72 to both sides, resulting in -9y = 54. Dividing both sides by -9, we get y = -6.
Thus, the final answer is x = -9, y = -6.