high school level student is asking ```y=4x x=-4y x+y=5 3x+2y=20 y=x-1 3x-y=4 x+y=3 2x-3y=-9 x+5y=4 3x+15y=-1 x+4y=8 2x-5y=29 2x-3y=-24 x+2y=15 x-5y=10 2x-10y=20 4x+y=0 x+2y=-7 ``` i tried divideing the two last numbers then subtracting the answer with the first number and i got them all wrong!!!! Hi, For the problem y = 4x x + y = 5 the first equation tells you that y and 4x are the same. Thus, where you see y in the second equation you can replace it by 4x. Thus you get x + 4x = 5 In other words 5x = 5 and thus x = 1 Now use the first equation again. y = 4x and x is 1. Hence y = 4. Thus the answer is x = 1 and y = 4. In the problem  x + 4y = 8 2x - 5y = 29 I see that the coefficient of x in the first equation is 1 and the coefficient of x in the second equation is 2. I would like the coefficient of x in both equations to be the same. I can accomplish this by multiplying both sides of the first equation by 2. That is 2(x + 4y) = 2(8) or 2x + 8y = 16 Thus the original two equations are equivalent to 2x + 8y = 16 2x - 5y = 29 The reason I wanted the two coefficients to be the same is that if I now subtract the two equations the coefficient of x becomes zero. That is (2x + 8y) - (2x - 5y) = 16 - 29 hence 2x + 8y -2x + 10y) = -13 Thus 18y = -13 and thus y = -13/18 Finally go back to either of the two equations you started with, replace y by  -13/18 and solve for x. Now try the others. Cheers, Penny Go to Math Central