So, you need to know that the slope stays where it is, and that the 6 is not part of the final answer, so get rid of it.
y=2x+b
Now, submit x in for x, and y in for y.
3=2(1)+b
3=2+b
1=b
Put this in for the equation missing the b,
y=2x+1
Now check it; if you put 1 in for x, does y=3?
