y=x+1
3x+y=21
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-x+y=1
3x+y=21
First do this. Change one (or both) of the equations so that the x and y are on one side, and the number is on the other. Make sure either the x or the y is the same in both equations (in this case, y) and then take one away from the other. The y will cancel out so you can work out x.
3x+y=21 -
-x+y=1
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4x = 20
x = 5
Then add the x into one of the two equations to find out y.
3x + y = 21
(3*5) + y = 21
15 + y = 21
y = 6
To check, put both x any y into the other equation.
-5 + 6 = 1
If the answer is correct, you have correctly solved the equations.
x = 5
y = 6
:D
