$A,B,C$ are three towns forming a triangle. A man has to walk from one town to next town, then ride to the next town then again drive towards his starting point. He can walk,ride,drive a km in $a,b,c$ minutes respectively. If he starts from $B$, he takes $a-b+c$ hrs, if he starts from $C$ he takes $b+a-c$ and if he starts from $A$ he takes $c+b-a$ hrs. The length of the triangle is: (assume the motion in anticlockwise direction)
- $60a$
- $50a$
- $40a$
- $65a$