Question

SOLVE EACH SYSTEM USING SUBSTITUTION

Answer 1

1. since the equations equal each other 
2x+19=x+7
-x        -x
x+19=7
  -19  -19
x= -12
sub into y= x+7
y= -12+7
y= -5

2. x+2y=-7
x+y+23=0
i don't know what the second equation is equal to, i'll assume 0

2y=x-7
y=1/2x-7/2
sub this into x+y+23=0
x+1/2x-7/2+23=0
3/2x+39/2=0
       -39/2   -39/2
3/2x= -39/2
x=-39/2 / 3/2
x= -13
sub into y=1/2x-7/2
y=1/2(-13)-7/2
y= -10

3. x+5y=2
x=-4y+5
sub x=-4y+5 into x+5y=2
-4y+5+5y=2
y+5=2
  -5  -5
y= -3
sub y =-3 into x =-4y+5
x=-4(-3)+5
x= 17

4. 3x+y=9
y=-5x+9
sub -5x+9 into 3x+y=9
3x+(-5x+9)=9
3x-5x+9=9
-2x+9=9
     -9  -9
-2x=0
x=0
sub into y=-5x+9
y=-5(0)+9
y=9