Question 882791
You need to know how fast they are walking. 
The amount of weight they're carrying doesn't matter other than it can change how fast they walk. 
So pick a speed in feet/sec would be convenient. 
Then once you know that 
{{{t=D/R=175/R}}}{{{sec}}}
So divide the distance (175 feet) by the speed (R feet/sec) to get the number of seconds it takes. 
Average walking rate is about 5 ft/sec.
At that rate, it would take {{{175/5=35}}}{{{sec}}}.