distance=240 km

let time= x hr

time speed= 240/x km/hr

new speed= (240/x)-20 kn/he

new time= x+1 hr

but distance is same = 240 km

so

240=((240/x)-20))*x+1

on solving.

x=3 or -4

-4 not-possible

time =3 hr.

initial speed = 80 km/hr

new lower speed =(80-20)km/hr=60 km/hr.

i guess thats the answer?