I presume the last part in a) is rad/s?

a) Angular speed is measured as "angle per time." We know it makes three revolutions (rotations) in one minute. The rest is unit conversion.

Then another unit conversion:

Since the time is in minutes, let's use the angular speed in rad/min. We know that the angular speed is constant, so the angle swept out by the child is

Then the distance traveled will be

-Dan