Question 757534
50 kms in 90 mins = ave speed of 33.3 kmph
Total of kms = 120 kms
120 kms/x = 50 kmph
Cross multiply 
x = 120 kms/50 kmph = 2.4 hours
2.4 hours = 2hours 24mins.
2 hours 24 mins. - 90 mins
= 54 mins.
This is the amount of time
required to complete 70kms
to achieve an overall average 
speed of 50 km/hr.
Hope this helps.
:-)