Let the speed of A be ‘a’ and speed of B be ‘b’.

Given, A takes 3 hours more than B to walk a distance of 30 km. But, if A doubles his pace (speed) he is ahead of B by hours

-------- (1)

------ (2)

Adding (1) and (2)

⇒ 15/a = 4.5

⇒ a = 150/45 = 10/3 km/hr

Thus,

⇒ b = 5 km/hr