Using the substitution method

Question

I have two questions that involve using either the elimination or substitution method and i need which method and how

 

1.  4x-7y=3

x-7y=-15

 

2. 3x+2y=-15

x-2y=19

Answer 1

For #1: Using substitution, solve the second equation for x or y. I'll solve for x. 

Add 7y to both sides, to get x alone. x=7y - 15. Then substitute that in for x in the first equation.

4(7y-15) -7y = 3

28y -60 -7y =3

21y = 63

y = 3

 

For #2: Using elimination, add the second equation to the first, to get rid of the 2y.

 

3x + 2y = -15

 x  - 2y  = 19

4x + 0   =  4

 x = 4