Question 1168709
ave speed=x
x=156/t, where t is time in hours.
(x+5)=168/t, same t

so tx=156 and t=156/x
and t=168/(x+5)
set those equal
168x=156x+780
12x=780
x=65 mph original speed and takes 2.4 hours
drive 70 mph and go 168 miles in that same time interval.

the answer is 65 mph.