Question

i have to do systems by substitution practice
ex -2x + y =-16
-8x - 7y = -20

Answer 1

-2x+y=-16

-8x-7y=-20

Solve -2x+y=-16 for y

Add 2x  to both sides

-2x+y+2x=-16+2x

y=2x-16

Substitute 2x-16 for y in -8x-7y=-20

-8x-7y=-20

Simplify both sides of the equation

-8x-7(2x-16)=-20

Add -112 to both sides

-22x+112+-112=-20+-112

-22x=-132

Divide both sides by -22

-22x/-22=-132/-22

x=6

Substitute 6 for x in y=2x-16

y=2x-16

y=(2)(6)-16

Simplify both sides of the equation

y=-4

Answer :

y=-4 and x=6

I hope that's help !

-22x+112+

Answer 2

This one's a little bit harder but i'm sure i can solve it. I usually pick the smaller number to solve first and then substitute the larger one.
-2x+y=-16
-8x-7y=-20

So you'll solve

-2x+y=-16
+2x/     +2x
y=2x-16------- this is what y means so you substitute y in the other equation for this answer.

-8x-7y=-20
-8x-7(2x-16)=-16------------------------Use distributive property to simplify.
-8x-14x+112=-16
-22x+112=-16
       -112    -112
-22x=-128---------------Divide -22 on both sides
x=5.82