Figuring Vacation and sic time for part time eomployees

I am trying to come up with a formula that will accrue a sick day for every 173 hours worked. When the hours hit 173, I need it to go back to zero to start over and to put those added days under accrued. I have come up with a formula that allows me to give 1.54 hours vacation for every 40 hours worked. But I think there has to be an easier formula than the one I came up with. Any help will be greatly appreciated.