2x + 4y = 205
3x + 8y = 342.50

We can make the y terms cancel by multiplying
the first equation by -2, to make the + 4y
become - 8y so it will cancel with the + 8y
in the second equation:

-4x - 8y = -410
 3x + 8y =  342.50     Then we add the equations term by term:
------------------
 -x      = - 67.50
       x = 67.50

We can make the x terms cancel by multiplying
the first equation by -3, to make the 2x
become -6x, and multiply the second equation 
by 2 to make the 3x become 6x so the -6x will 
cancel with the 6x in the second equation:

-6x - 12y =  -615
 6x + 16y =   685     Then we add the equations term by term:
------------------
       4y =    70
        y = 17.50


Edwin