Question 875132
D = rt.  Distance = rate times time.<P>
t = Distance / rate.<P>
Their rate distance increase is 60 + 30 = 90 mph.  The distance between them increases by 90 miles every hour.<P>
The desired distance is 150.<P>
150/90 = 5/3 = 5 and 2/3  hours = 1 hour 40 minutes.