X=15
Hope this helps I had the same problem. That’s what I got.
Y=mx+b
lines are parallels so m=2
y=2x+b
line passing through the point (4,2), so x=4 y=2
put these value in equation
2=2*4+b
2=8+b
b=2-8
b=-6
y=2x-6
Answer: y=2x-6
(verification on the picture)