Two men standing 15 km apart on a highway started to walk toward each other. First man walks for 2.5 km straight then take a right turn and walks for 1.5 km. He then turns left and walks for another 2.5 km and then takes the direction back to reach the highway. In the meantime, the other man can only travel 3.5 km along the highway. What would be the distance between them at this point? (in km.)

a) 6.5
b) 7.5
c) 8.5
d) 9.5