Question 1000000
4x-y=-1 
subtract 4x from both sides

4x-4x-y = -1-4x

-y =-1-4x

divide by -1

y=4x+1

If you observe the original equation

when you take any term on the other side of the equation the sign changes from + to - OR - to +
2x+4y = 13

2x+4(4x+1) =13
2x+16x+4=13
18x=13-4  ( The sign of 4 has changed bcause I brought it on the right side)

18x=9

/18
x=9/18
x=1/2

plug x



2x+4y=13