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

Step 1. Take one equation and make either x or y the subject of the formulax=9+3y, 5x+y=21Step 2. Substitute in the equation5(9+3y)+y=21Step 3. Make y the subject of the formula45+15y+y=21 (multiplied out the brackets)16y=-24 (Subtracted 45 from both sides)y=-24/16 (Divided by 16 on both sides)y=-3/2 (Scaled the fraction down) Step 4. Find out what x is equal tox=9+3(-3/2)x=4.5 or 9/2