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

To solve simultaneous equations we want to use only one variable so either x or y. Therefore we need to eliminate (get rid of) one of the variables .If you multiply x - 3y = 9 by 5 you will get 5x - 15y = 45 (make sure you multiply every term by 5). Now we have two equations that have the same number of x.To eliminate x subtract 5x + y = 21 from 5x - 15y = 45.(I would show this on a whiteboard) The answer is 16y = -24So to find y divide -24 by 16. (again would be shown on a whiteboard until the faction is simplified)y= -3/2Having found y, we now must substitute it into one of the original equations so find x.I would chose 5x + y = 21 because then we don't have to multiply up a y value.5x + (-3/2) = 21Then I would show on a whiteboard how I would rearrange the formula into 5x = 21 + 3/25x = 45/2x = (45/2)/5 x = (45/2) x (1/5)x = 45/10x = 4.5