On two circular tracks, arcs of equal length 10m are marked. Track P has radius 20m and track Q has radius 40m. Which statement about the angles subtended by the two arcs at their respective centres is correct?
a) Both tracks subtend the same angle.
b) The arc on track Q subtends twice the angle subtended on track P.
c) The arc on track P subtends twice the angle subtended on track Q.
d) The arc on track Q subtends four times the angle subtended on track P.