Greg and Darius earned $12.50 an hour for 9 hours of work? if they each got half and Greg spent $15 on a shirt, how much does he have now?

Assuming that the wage of $12.50 an hour applies to Greg and Darius as a team instead of individually, 9 hours of work would have gotten them:

$12.50/hour * 9 hours = $112.50

If they split the wage in half among themselves, then Greg would have

$112.50 : 2 = $56.25

such that if he spent $15 of it (assuming that's the only money he has), he would now have:

$56.25 - $15 = $41.25

∴ Greg now has $41.25.