In a 500 m race, the ratio of the speeds of two contestants A and B is 3 : 4. A has a start of 140 m. Then, A wins by: Choose the correct choice from the following:
A) 60 m
B) 20 m
C) 43 m
D) 20 m
E) 23 m

Rationale: "to reach the winning post a will have to cover a distance of ( 500 - 140 ) m , i . e . , 360 m . while a covers 3 m , b covers 4 m . while a covers 360 m , b covers 4 x 360 m = 480 m . 3 thus , when a reaches the winning post , b covers 480 m and therefore remains 20 m behind . a wins by 20 m . answer : d"
Answer: D