z equals -1 because 8 time negative one equals negative 8 plus 8 equals 0
I think its B but ima have to check again and get back to you
Answer:
slope intercept form is y=mx+b
your m is 4
all you do is plug the numbers in
y=4x+6
and 
use the second expression to calculate the left-hand side of the first equation:

Add 10 to both sides if this equation to get

and divide both sides by 2

this proves that x = 17, give the two initial equations