Let h be the number of hours a day she does community service.
She has to make up 50-38=12 hours to get to 50 hours from 38 hours.
If d is the number of days then dh≥12. We can write d≥12/h to work out the number of days in terms of the hours per day, or we can write h≥12/d to work out the number of hours per day she would need to work in terms of the number of days she has to complete the hours.
Also if H=hd, the number is hours required, then H≥12 hours.