determine the resulting equation if one variable is solved in terms of the other variable in one equation and substitute this variable in the other equation.
1.) x=-y+7
x-y= -9
2.) y=2x
4x +3y=20
3.) y=2x +5
3x-2y=5
1. you know that x=-y+7 so you are going to take that and substitute/put it in for x in the followin equation
(-y+7)-y=-9
2. in this equation we know that y=2x,
4x+3(2x)=20
4x+6x=20 10x=20
divide both sides by ten and you get x=2
3. y=2x+5
3x-2(2x+5)=5
3x-(6x+10)=5
-3x+10=5 subtract 10 from each side
-3x=-5 divide both sides by -3 to get answer
I'm pretty sure I did this right but no guarantees :)
Hope this will help you get the idea