#10y=42+2x" (1)"#
#"expand the second equation by 10"#
#y=3/4x+3" (2)"#
#color(red)10*y=color(red)10*(3/4x+3)#
#10y=30/4x+30" (3)"#
#"so left side of the equations (1) and (3)are equal"#
#"we can write:"#
#42+2x=30/4x+30#
#2x-30x/4=30-42#
#(8x-30x)/4=-12#
#-22x=-4*12#
#22x=48" "x=48/22#
#x=24/11#
#" now use the equation (1)"#
#10y=42+2(24/11)#
#10y=42+48/11#
#10y=(462+48)/11#
#y=(51cancel(0))/(11cancel(0))#
#y=51/11#