A car moves a distance of 200 m. It covers first half of the distance at speed 60 km h^-1 and the second half  at speed $\mathrm{v}$ . If the average speed is 40 km h^-1 , the value of $\mathrm{v}$ is

• A

  30 km h^-1

• B

  13 km h^-1

• C

  60 km h^-1

• D

  40 km h^-1