Question 14183
you have 2 choices to solve this equation. 1. substitution 2. graphing  
SUBSTITUTION
{{{y=-2/3x}}}
{{{4y=-x+15}}}
Plug in Y in the second equation
{{{4(-2/3x)=-x+15}}}
{{{-8/3x)=-x+15}}}
isolate the X value
{{{-5/3x=15}}}
solve for x by multiplying both sides by -3/5 (the reciprocol)
{{{x=15*(-3/5)}}}
{{{X=-9}}}
Now plug X back in the original equation. 
{{{y=(-2/3)*-9}}}
{{{y=6}}}
your ordered pair would be (-9, 6)
GRAPHING
convert both equations into y=mx+b form
you already have one:
{{{y=-2x/3}}}
You can convert by making the "y" stand by itself
{{{4y=-x+15}}}
divide both sides by 4
{{{y=-1x/4+15/4}}}
Then graph them. 
{{{graph( 300, 200, -10, 10, -10, 10, -2x/3, -1x/4+15/4)}}}
Then you can either tell the intersection point on a graph of the two lines, or you can substitute.