the info about the trip from Malim to Petani is irrelevant and only there to confuse us.
but from the return trip info we get all we need.
for x km it took then 30 minutes at an average speed of 105 km/h.
to get km out of km/h, we need to multiply the speed number by the hours traveled. that removed the "h" and leaves us with km.
n km/h × a h = a×n km
so, now, in our example we have 105 km/h, and 30 minutes = 1/2 h.
so, we have
x = 105 km/h × 1/2 h = 105/2 km = 52.5 km