I know this topic is old, but you want to make $45 per man hour. Since you have a helper then you should be billing $90 per hour. You don't want to just add his cost to your $45 hour goal because not all of his payroll will be billable (drive time, etc), plus why would you want to provide a laborer to cut hours with no gain to yourself.
Don't forget that it probably cost you more money to obtained enough work to keep your helper busy (advertising, time giving bids, etc.), so why give him away at cost. You might as well just do half the amount of work and work solo.
Bottom line is when looking at a job determine how many man hours it will take. Remember that with 2 guys working each hour is really 2 hours, then charge $45 an hour plus materials and any other direct cost related to the job. So if you looking at a job and saying you and your helper can do it in 5 hours then is reality you are working 10 man hours. That would be $450 pls cost.
Your paying a pretty good wage for only charging $45 per man hour. A good rule of thumb is that each employee should generate 6 times their hourly pay to cover their total cost to you and bring in a decent net income off of them. A worker will cost you more then their hourly wage. It's like having an extra person living in your house, they use more resources, plus you have things like WC, unemployment etc.