Given:
[1]#color(white)("XXX")-5x-5y=-6#
[2]#color(white)("XXX")3x-y=-1#
Rearrange [2] to isolate the #y# term on the left side:
[3]#color(white)("XXX")-y=-1-3x#
(the next two steps are not necessary, but I find it easier to work with positives)
Multiply both [1] and [3] by #(-1)# to reverse the signs
[4]#color(white)("XXX")5x+5y=6#
[5]#color(white)("XXX")y=1+3x#
Substitute #(1+3x)# from [5] for #y# in [4]
[6]#color(white)("XXX")5x+5(1+3x)=6#
Simplify [6]
[7]#color(white)("XXX")20x+5=6#
Subtract #5# from both sides of [7]
[8]#color(white)("XXX")20x=1#
Divide both sides of [8] by #20#
[9]#color(white)("XXX")color(green)(x=1/20)#
Substitute #1/20# from [9] for #x# in [2]
[10]#color(white)("XXX")3xx1/20-y=-1#
Subtract #(3/20)# from both sides of [10]
[11]#color(white)("XXX")-y=-23/20#
Multiply both sides of [11] by #(-1)#
[12]#color(white)("XXX")color(green)(y=23/20)#
