Michael lives 1 block west and 2 blocks south of the southwest corner of City Park. His office is 1 block east and 3 blocks north of the northeast corner of City Park. On workdays he walks on streets to the southwest corner of City Park, then takes a diagonal path through the park to the northeast corner, and then walks on streets to his office. If his route is as short as possible, how many different routes can he take?
6
9
10
12
15
