Andrea tutors two high school students during the week. She tutors each student 4 days a week for 45 minutes a day. Which of the following equations can be used to calculate the number of minutes Andrea spends tutoring in x weeks?
 A. 
 y = 540x
 B. 
 y = 45x
 C. 
 y = 360x
 D. 
 y = 180x