There is 24 hours in a day and you need to rest for 10 hours a day, so working hours = 14 hours
There is 60 minutes in one hour so if you count one dollar per sec,
14 hours/day x 60 min/hr x 60sec/min x $1 / sec = $50,400
So you can count $50,400/day and when there is $5 billion which is equal to = $5,000,000,000
And there is 365 days in a year so,
$5,000,000,000 / ($50,400/day) = 99206.35 / 365 = 271.8 years