**Concept:** **The question tests on the basics of Rates(Time Speed)**

**Solution:**

Let the correct time taken by Dimpy = t hours

By the law of proportions, when distance is constant s1 * t1 = s2 * t2

s1 = 10 km/h and t1 = (t + 7/60) (Converting minutes to hours)

s2 = 12 km/h and t2 = (t - 8/60)

Therefore 10 * (t + 7/60) = 12 * (t - 8/60)

10 t + (70/60) = 12t - (96/60)

166/60 = 2t

t = 83/60

Putting t in any of the equations will give us the distance.

10 * (83/60 + 7/60) = 10 * 90/60 = 15 km**Option A**