9 km/hour

10 km/hour

11 km/hour

12 km/hour

D. 12 km/hour

We need to calculate the distance, then we can calculate the time and finally our answer.

Lets solve this,

Let the distance travelled by x km

Time = Distance/Speed

$\frac{x}{10}-\frac{x}{15}=2$

$(because,2pm-12noon=2hours)$

$3x-2x=60\therefore x=60.$

$Time=\frac{Dis\mathrm{tan}ce}{Speed}$

$Time@10km/hr=\frac{60}{10}=6hours$

So 2 P.M. - 6 = 8 A.M

Robert starts at 8 A.M.

He have to reach at 1 P.M. i.e, in 5 hours

So, Speed = 60/5 = 12 km/hr