Acompany does research on their product and finds that three-fifths of people who try the product, use it again. if 400 people try the product, how many would we expect to use it again?

What is the missing step in this proof ?

Write the equations in logarithmic form 9^4=6,561

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?