Tina works no more than 30 hours at a nail salon each week. She can do a manicure in 20 minutes and a pedicure in 30 minutes. Each manicure earns her $25 and each pedicure earns her $40, and she must earn at least $900 to cover her expenses. If during one week, she does enough manicures m and pedicures p to cover her expenses, which of the following systems of inequalities describes her working hours and her earnings?
A) 3m+2p≤ 30
25m+40p≥ 900
B) 2m+3p≤ 30
25m+40p≥ 900
C) m/3 + p/2 ≤ 30
25m+40p≥ 900
D) m/3 + p/2 ≥ 900
25m+40p≤ 30