Mr. Roger want to buy a car, he signed a loan of money contract with Mr. Tom to borrow 900,000 Baht from Mr. Tom and to return to Mr. Tom the money after twelve months from the date of signing the contract. Mr. Paul verbally guarantee for the debt payment. In this loan of money contract both of Mr. Roger and Mr. Tom agreed that the interest was payable, but did not specify and interest rate amount in the contract