A motorcicle and a truck left the town at the same time .After travelling in the same direction for 1 and a quarter hours , the motocicle had...

Since we know the average speed of the motorcycle and the
time, we can compute the distance it had travelled.

We know
that the distance is the product of the speed and
time.

distance =
speed*time

distance = 60(Km/hr)*1.25
hr

distance = 75 Km

We also
know, from enunciation, that the motorcycle travelled 25 Km farther than the truck,
after one and a quarter hours.

The distance travelled by
the truck, after one and a quarter hours, is the difference between the distance
travelled by the motorcycle and the amount of 25
Km.

distance = 75 - 25 =
50Km

Now, we can compute the average speed of the truck,
since we know the distance travelled and the time:

av.
speed of truck = distance/time

av. speed speed of truck =
50Km/1.25 hr

av. speed speed of truck = 40
Km/hr