Shelby works as a bus driver. If Shelby worked for 3 days and earned $300, how much did she earn per day?
To find out how much Shelby earned per day, we need to divide the total earnings, $300, by the number of days she worked, which is 3.
$300 / 3 = $<<300/3=100>>100 per day
Shelby earned $100 per day. Answer: \boxed{100}.