Solve the simultaneous equations: 5x + y = 21 and x - 3y = 9

label equation 5x + y = 21 as (1) and equation x - 3y = 9 as (2) multiply equation (2) by 5 to get : 5x - 15y = 9 (3) then subtract equation (1) from equation (2) in order the eliminate the x variable -16y =24 solve for y: y = -3/2 then substitute the value for y =-3/2 into the first equation and solve for x to determine: x=9/2