[MrWalrus]

Ok, so that bill thing is kinda confusing. I'll make the whole system easier.

If you invest any amount of money, you can get a 4% return on the amount after 30 days, 9% after 60, or 16% after 90.

So if you invest $1,000, you can get back $40 in 30 days, versus $8 from the bank.