You're forgetting the chain rule. Remember when you take take the derivative of that, you need to multiply it by the derivative of the inside. So, compensate for that when integrating by multiplying it by 1/(derivative of inside). The key here is noticing that the derivative of the inside (2x+4) is 2(x+2), notice the x+2 on the outside and you're all set. Feel free to ask me for any more help?