Hello, I have been having trouble with these 3 questions that are on my upcoming test. I have tried it many times without getting an answer and I could really use some help.

Here are the questions:

1)

2x - 3y = 5

4y + 2z = -6

5x + 7z = -15

Solve for X Y and Z using substitution or elimination.

EDIT :I Recently tried to use a homework help online service who gave me the answer ( I didnt understand their work though) For this they got x=4 y=1 and z=-5

2)

2x + 3y - z = 9

x - 3y + z = -6

3x + y - 4z = 31

Solve for X Y and Z using substitution or elimination. (Same as before)

3)

6/x - 4/y = 1

-3/x + 3/y = 2

Solve for X and Y (6/x, 4/y , -3/x and 3/y and fractions) using substitution

EDIT: Same homework help (Once again Didn't Understand what the heck their work meant but..) They Got for X=6/11 and Y=2/5

Thank you in advance and please show your work so I can understand it.

MOVED POST TO URGENT SECTION DUE TO TEST TIME CHANGE.