Main problems:

$($The $401$K problem$)$: At the end of each year I put $M$ dollars into a retirement

account that earns $3\%$ return at the end of each year.

$($a$)$ How much will I have in the the account at the end of $1$ year?

$($b$)2$ years?

$($c$)3$ years?

$($d$)$ How much will I have after $40$ years ${?}^1?$