The President of State University Wants to Forecast Student Enrollment

The president of State University wants to forecast student enrollment for this academic year based on the following historical data:
$$\begin{array} { | c | c | } \hline \text { Year } & \text { Enrollnents } \\\hline 5 \text { years ago } & 15,000 \\\hline 4 \text { years ago } & 16,000 \\\hline 3 \text { years ago } & 18,000 \\\hline \text { 2 years ago } & 20,000 \\\hline \text { Luast year } & 21,000 \\\hline\end{array}$$
What is the forecast for this year using a moving-average forecast based on the last four years?

A) 18,750
B) 19,500
C) 21,000
D) 22,650
E) 22,800