Another format for the derivative is:

y' = dy/dx, so:

dy/dx = 6x + 3

Now "multiply" both sides by dx:

dy = (6x + 3)dx

Now just plug the numbers in.

-Dan

PS The "multiplication" I did really isn't a multiplication. It's a looooong story. Suffice it to say we can get away with it, but have a care to check the truth of it before you do it.