Answer:
1. 5 hours
2. 4 hours
Reason:
Formula for speed is speed = 
, if you want to find time, then take distance / speed, which will equal to 100 / 20 = 5 hours, and the same with 2.
Subtract mm from both sides
-4=2m-m−4=2m−m
2 Simplify 2m-m2m−m to mm
-4=m−4=m
3 Switch sides
m=-4m=−4
