Answer:
1.5 hours
Step-by-step explanation:
First of all, this problem is a variation problem, not a distance problem, which means that the format should be:
1.8 : 3.5
x : 4.2 if x= how long it would take Max to cover the same distance walking at 4.2 km/h
Since they are inversely proportional, we have to multiply 1.8 by 3.5 and then divide the leftovers, which is 4.2 in this case, to equal 1.5 hours.
Glad if it helped!! :)