Question

can some one help how to work out this problem
x-y=11
2x+y=19
solve by substitution 

Answer 1

$x-y=11 \\ 2x+y=19 \\ \\ \hbox{solve the 1st equation for x:} \\ x-y=11 \\ x=11+y \\ \\ \hbox{substitute 11+y for x in the 2nd equation:} \\ 2(11+y)+y=19 \\ 22+2y+y=19 \\ 22+3y=19 \ \ \ |-22 \\ 3y=-3 \ \ \ |\div 3 \\ y=-1 \\ \\ x=11+y=11-1=10 \\ \\ (x,y)=(10,-1)$