Subject: mathqa
Question: yesterday it took robert 4 hours to drive from city a to city b . today it took robert 2.5 hours to drive back from city в to city a along the same route . if he had saved 15 minutes in both trips , the speed for the round trip would be 70 miles per hour . what is the distance between city a and city b ?
Option: 
A: 300
B: 120
C: 210
D: 90
Answer: C