#x-3y=-2, -2x+5y=-7#
#x-3y=-2##.................1#
#-2x+5y=-7.............2#
#2x-6y=-4#.....................3#=1 xx 2#
#-y=-11#............................#=2+3#
#y=11#
#5x-15y=-10#....................4#=1xx5#
#-6x+15y=-21.............5#= #2xx3#
#-x=-31#...............................=#4+5#
#x=31#
substitute # y=11,x=31 # in 1
#31-3(11)=-2#
#31-33=-2#
#-2=-2#