You can make use of the formula: distance = rate x time
On the main street, the tourists walked a distance of s km at a rate of v km/h. The time t is unknown, so we can call it t1
Plugging into the above formula gives us:
s = vt1
On the side road, the tourists walked a distance of 2s km (twice the distance walked on the main street), at a rate of (v - 2) km/h, which is 2 km/h less than the rate on the main street. Since the problem does not state that the amount of time walked on the main street and the side road is the same, then we will call the time walked on the side road t2. Using this info, we again plug into the formula to obtain:
2s = (v - 2)t2
You can now substitute the given values of s and v to solve for t1 and t2.