The correct option is B 48 km/h
Letx consider, x= total distance covered by the car,
Time taken to complete the half distance with velocity v=40km/h,
t1=x2×40=x80hr. . . . .(1)
The time taken to complete another half distance with velocity u=60km/h
t2=x2×60=x120hr
The total time taken, t=t1+t2
t=x80+x120=x48hr
The average speed of the car,
vavg=xx/48=48km/h
The correct option is B.