As Emily is riding her bicycle on a long straight road, she spots Emerson skating in the same direction 1 / 2 mile in front of her. After she passes him, she can see him in her rear view mirror until he is 1 / 2 mile behind her. Emily rides at a constant rate of 12 miles per hour, and Emerson skates at a constant rate of 8 miles per hour. For how many minutes can Emily see Emerson?
Answer Choices
A. 6
B. 8
C. 12
D. 15
E. 16