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

Call '5x + y = 21' equation 1 and 'x - 3y = 9' equation 2. To solve this, we need the coefficients of x in both equations to be the same or the coefficients of y in both equations to be the same.
Method 1 - solving for y firstMultiply equation 2 by 5 to get:5x - 15y = 45 (call this equation 3)Now we are going to take equation 1 away from equation 3: 5x - 15y = 45 - 5x + y = 21 which becomes: -16y=24Solve for y:y=-24/16 =-3/2Sub this value into equation 1 to solve for x:5x + (-3/2) = 215x = 45/2x= 9/2