Question

In Equation such as 6x-y=29
and then i have x=y-9 i sub in y-9


6(y-9)-y=-29
solve for y which then equals
6y-54-y=-29
5y=25 ( how does it get their from 6y-54-y=-29?)

Answer 1

and why

Answer 2

In the original equation you show 6x-y=29 and int the other equation you show
6y-54-y=-29. I assume it should be -29 and not 29.

6y-54-y=-29 Add 54 to both sides of the equation in order to group like terms:
6y-54-y+54=-29+54
6y-y=25
5y=25
y=5