A takes 4 hours more than B to cover a distance of 80 km.  If A doubles his speed, he takes 1.5 hour more than B to cover 80 km.  To cover a distance of 160 km, how much time (in hour) will B take travelling at the same speed?

2 hours

S_A (Speed of A) =    1    :    2

T_A (time of A)    =    2    :    1 ... (Diff. 1  → ×2.5 → 2.5 hours)

                              ↓    

                            ×2.5

                              ↓    

                          5 hours

as A takes 4 hours more than B to travel 80 km, i.e. B takes only 1 hour so S_B = 80 km/h

t = \(\frac{160}{80}\) = 2 hours