Answer:
x=2, y=13
Step-by-step explanation:
In order to get this by addition which is the easiest way for this you want to take both equations
y=3x+7 and y=-4x+21 and move x to the other side of the equation so it is like 4x+y=21 and -3x+y=7 like that now you have to get rid of one of the exponents and the easiest one to get rid of is y so I'm going to multiply -3x+y=7 by negative 1 so it becomes 3x-y=-7 that way the equations value has not changed since I multiplied both sides and now when I add
4x+y=21 and 3x-y=-7 It'll look like
4x+y=21
3x-y=-7 add those It will get rid of the y
then get 7x=14 simplify to get x=2 then you can take -3x+y=7 plug in x and get
-3(2)+y=7 multiply into -6+y=7 then simplify you get y=13
