Thirty minutes before a concert, there were 1,200 people in the 3,000-seat auditorium where the concert was being held. Five minutes before the concert, the auditorium was 90% full. Which of these equations can be used to determine p, the number of people who entered the auditorium during this time interval? A) 0.9p=3000
B) 0.9=1200+p/3000
C) 0.9(1200+p)=3000
D) 0.9=p/3000