不知道怎麼算出來的, 請好心人士幫忙!
The King School has an enrollment of 900 students. The school day at King consist of 6 class periods, each of which is taught by one teacher, and there is an average of 30 students per class. If each teacher at King teaches 5 of the 6 periods and has one period free, but no student has a free period, how many teachers does the school have?
(A) 25
(B) 30
(C) 36
(D) 60
(E) 150
