Simple profit + capital problem, need your help

Hey guys, newbie here. My maths (as we call it in the UK) sucks and need help with this little problem. I am going to be trading mineral commodities soon at a low level and need an income projection over 20 weeks

Here goes. Assuming i am buying a commodity and trading it as follows on a weekly basis

buying price --------------------------------------$25/unit

selling price --------------------------------------$37/unit

Roughly gross profit from above ------------------ $12/unit

So assuming i start off with capital of $2500 (to buy initial stock which will be 100 units = 2500/25 ), how much profit will i make in 20 weeks please if i am reinvesting $6 into the business to buy more stock (out of the $12 out of every unit). So i am reinvesting $6 for every $12 per unit. Please provide answer as well as the work sheet for every week till week 20 and also how much will i have as compound capital + profit after 20 weeks

I am buying stuff and selling it every 7 days by the way so keep that in mind, so its week 1, week 2 (2500 + profit from week1) right through to week 20

Thanks in adavance of your help(Bow)