Question 44067
You have 2 equations to start with:
{{{x - 2y = -6}}}     (..1)
{{{y = ((-3/2)x) -1}}}    (..2)
Rearrange equatiom (..2) to give x in terms of y: 
{{{x=2y-6}}}          (..3)
Now substitute equation (..3) into equation (..2) for x:
{{{y=((-3/2)(2y-6))-1}}}
{{{y=-3y+6-1}}}
{{{4y=5}}}
{{{y=5/4}}}           (..4)
Now substitute equation (..4) into equation (..3) for y:
{{{x=2(5/4)-6}}}
{{{x=10/4-6}}}
{{{x=2.5-6}}}
{{{x=-3.5}}}

I hope this helps 
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk