for me i think the easiest way is to use matrices:
[tex] \left[\begin{array}{ccc} \frac{3}{7}& \frac{-5}{8} & 33 \frac{1}{3}\\64&-17& 12\frac{1}{2} \end{array}\right] [/tex]
you get,
x = -17.08
y = -65.05
you can also multiply one of the equations by a number so that either y or x can be cancelled so you can find one..then all that's remaining is to substitute the value of what you got first(be it y or x) into one of the equations