Complete parts (a) through (c) below. (a) At mail time, you receive a check for $26 and an envelope with neither a bill nor a check. What addition-by-0 fact has been illustrated? (b) At mail time, you receive a postcard from your friend and a bill for $25. What addition fact is illustrated? (c) What is illustrated if your mailbox has a bill for $10 and a check for $10?