<human>: Condense the text into a few key points

Hi all,
Sorry for this wall of text...

So I have been working at my current job for a little over a year now. It is an hourly position that started when I was in college. I would work 20 or so hours a week.

Fast forward, college didn't work out for financial reasons, but I have still been working at my job, only more of a full time role. I have been looking for a new job with salary and benefits. Enter my dilemma.

I interviewed with Company A on 6/5. They really liked me, but I got in through a reference and the job I interviewed for wasn't posted on their site yet. Due to this, they told me they would like to interview other candidates after they officially posted the job, but they told me that they didn't believe any candidate would be "head and shoulders above me." The one who would be making the decision told me that my salary would most likely be low to mid 40's. He was on a business meeting in Vegas the past week and a half, so they only started doing interview this week.

After the interview with Company A, Company B called me. I interviewed with them on 6/10. I just received a letter today stating that I had got the position. The starting salary is 40k, and I have until the end of the day on Monday to inform them of my decision.

Honestly, I would be happy in either position. I was wondering how I can use my offer that I officially received from Company B to possibly fast track an offer from Company A, and in turn possibly negotiate the 40k salary with Company B. I DO NOT want to get too greedy with this, and that is why I came here.
<bot>: Interviewed at 2 companies. Got an official offer from one and want to try and use that to fast track an offer from the other, because (not to sound cocky) I know they want to hire me.