Ineed , you need to find x and y
step by step would be good

X + 2y = 3 (1)
x - y = 6   (2)

Equation (2) - (1) :
-3y = 3                         //  ║x - x = 0 ║;║ - y - 2y = -3y║ ; ║6 - 3 = 3 ║

y  = -1                          //   ║ ÷ (-3) on both sides ║

Substitute y = -1 into equation (2) :

x - y = 6                        //   ║ Equation 2║

x - ( -1 ) = 6                   //   ║ Sub y = -1 into the equation║

x + 2 = 6                       //   ║ open the bracket ( - ) ( -) = +  ║

x = 4                             //   ║ Take away 2 from both sides║

x = 4, y =  -1