In order to find the distance from the horse to the center of the merry-go-round, first let's convert the angular speed of 2.5 rev/min to rad/seconds:

Now, in order to find the distance (which is equivalent to the radius of the circle), we can use the formula below:

Where v is the linear speed, w is the angular speed and r is the radius.
So, for v = 3.2 and w = 0.2618, we have:

Rounding to the nearest tenth, we have a distance of 12.2 feet.