The distance between two cities is one hundred miles, and a woman drives from one city to the other at a rate of fifty mph. at what rate must she return if the total travel time is three hours and forty minutes?

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

b, i believe, but not sure.