Given the task definition and input, reply with output. You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

Question: In covering a distance of 36 km, A takes 2 hours more than B. If A doubles his speed, then he would take 1 hour less than B. A's speed is:

 Option A: 5 km/h

 Option B: 6 km/h

 Option C: 10 km/h

 Option D: 15 km/h

 Option E: 25 km/h

Option B