(amount of USD x (15000 + (100 x amount of USD))) = amount of TC
In more simple terms, the amount of TC received is a normal $1 = 15000TC exchange rate with an added bonus depending on the amount of cash spent. This means that, if you bought $10 worth of TC, you would get a $1 = 15000TC rate, with an added 1000TC, meaning that the rate is $1 = 16000TC. This would mean that you would purchase 160000TC, a much better rate than all other TC sellers.