B is just loaning money, fully secured and will get his money back? Then no equity, and a high interest rate. If you want to, you can offer a token amount of equity (below 1%) to sweeten the deal.
EDIT: after all the clarification, the remaining question is how much value A provide. A will be the CEO I assume, since B is not taking any role in the business, part from providing financing and the loan. If A is repleceable and B could start the same business with pretty much anyone, then you can imagine an 80/20 split in favor of B. But the reverse is true as well: if A is critical and B couldn't start anything without A, then it could go anywhere from 75/25 for A, to 50/50.