The correct option is (B) 320 cm.
Explanation:
Let jockey divider 600cm length into two parts as shown
Let the jockey be placed at a distance y cm from the left.
∴ [y / (600 – y)] = [(15 – x) / x] = [(15 – 7) / 7] = (8/7)
∴ 7y = 4800 – 8y
∴ 15y = 4800
y = 320 cm
∴ distance is 320 cm from point A.