Question 133055
Let d = distance and t = time to arrive 

d/(t+1/2)=36
d/(t-1/2)=42

then

36(t+1/2)=42(t-1/2)
36t+18=42t-21
-6t=-39
t=13/2=6.5
d=36(13/2+1/2)=36(7)=252

Answer: distance = 252 kms