Doubting if one has settled his accounts during his student days

Q: A person has been attending a madressa. At the madressa there is a tuck shop which allows the students to take things on credit. As a student many things were bought on credit and paid later. A few years later the student has doubts in their mind as to whether they have paid their accounts accordingly. What can the person do besides asking Allah for forgiveness?

Working as a teller in the bank

Q: I have a job interview working for a bank in the USA. I was told that it is haraam to work for an American or foreign bank because they deal with interest rates (RIBA). However when I work there I will be at the cashier, depositing the clients money in their account, not directly with riba. Please advice if this is haraam or halaal?

Khilaal of the toes

Q: Regarding khilaal of the toes, should one make khilaal of the toes of both feet together after washing both the feet or should one make khilal of the toes of the right foot after washing the right foot and of the left foot after washing the left foot? What is the sunnah method?