A searchlight rotates at a rate of 3 revolutions per minute. The beam hits a wall 10 miles away and produces a dot of light that moves horizontally along the wall. How fast is this dot moving when the angle `theta` between the beam and the line through the searchlight perpendicular to the wall is `pi/6` (that is, `30^@`)? Note that `dtheta/dt = 3(2pi) = 6pi`.