I buy and sell airtime online but need help with the numbers

There's not much of a margin and I need to know if I am doing the right thing. I have tried to calculate this problem myself but have found it a bit hit and miss. I wonder if anyone can help. All prices are in Kenya Shillings (KSh) as I live and trade in Kenya. I sell airtime online (note to forum admin - if I was advertising I would probably post a link here).

I buy airtime at 5.75% discount and sell it at 2% discount

eg KSh 1000 airtime is bought at KSh 942.5 and sold at KSh 980

The payment processor (a Local bank) take 3.5% of the sale price (the KSh 980).

I want to be able to do all this without leaving the comfort of my office so can buy airtime remotely from a local company but that involves sending money by bank transfer at a charge of KSh 350, which wipes out a lot of profit.

The thing is, this is a fixed cost, unlike the percentages previously mentioned.

The questions is... what is the minimum I can transfer and still break even once that value of airtime is sold?

I have tried putting in numbers and working through it by guesswork but I would be very impressed if someone could come up with a formula or something.

Thanks

*edit* Is it 109375 ?

980-942.5 = 37.5

980 x 0.035 = 34.3

37.5 - 34.3 = 3.2

350/3.2 = 109.375

as that was an example using KSh1000 airtime the answer must be multiplied by 1000.

Is that right?

*edit (2)*

If the above IS correct dropping the sales discount to 1% has a big impact on the amount I have to commit. Using the same calculations as above it means I now only have to transfer a minimum of KSh 27000 to break even....I think