On the Initial Day of Class (I

Multiple Choice

On the initial day of class (i.e. N=0 ) , a professor counts 690 students as being present in her math class. On the 6^th day of class (i.e. N=5 ) the professor counts 450 students as being present in her math class. If the number of students decreases in a linear fashion, what is the common difference d ?

A) -6
B) -18
C) -36
D) -48
E) None of the above.