Several logs are stored in a pile with 22 logs on the bottom layer, 21 on the second layer, 20 on the third layer, and so on. If the top layer has one log, how many logs are in the pile?

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?