It's called "solve the equation for 'y' ". That means move things
around so that you end up with 'y' all alone on one side, and
everything else on the other side.
You started with 9x - 7y = -7
Subtract 9x from each side: - 7y = -9x - 7
Divide each side by -7 : y = 9/7 x + 1