Answer:
If Xmart doesn't notify Fred that Donald is not there agent anymore, then any agreement made between Donald and Fred will be valid and binding to Xmart.
Donald is no longer Xmart's agent, but unless Fred is notified, he still may act as an apparent agent. Apparent agents are people that someone could assume are acting on behalf of a principal, e.g. a person that wears a store's uniform inside a store is presumably a salesperson or someone that works for the store, therefore, he/she is an apparent agent. You do not ask for employment contracts when you enter a store.