Final answer:
The man's velocity relative to a stationary observer is the sum of his walking speed and the speed of the sidewalk moving in the same direction, totaling 13 mi/h east.
Step-by-step explanation:
The man's velocity as observed by a lady standing next to the moving sidewalk is the sum of his velocity and the sidewalk's velocity. Since both the man and the sidewalk are moving east, their velocities add up. The man's walking speed is 1 mi/h east, and the sidewalk's speed is 12 mi/h east. By adding these together, we get a total velocity of 13 mi/h east.