well in her first travel (when she goes to the anther city)
v1= 50mph
d1=100 m
t1=?
t=d/v=100/50=2h
that's meat that she will take 2hours during the first travel
and total travel time = 3h
she wants to take only 1 h in her second travel
v2=?
d2=100 m
t2= 1h
v2= d2 *t2 =100mph
total travel time is 3 hours and 40 minutes so i belive the correct answer is 60mph