Lets assume total distance = 2d.
we need to calculate 2d/4 = average speed for entire trip.
statement 1: tells us that bus travel 50MPH for first 2 hrs... clearly not sufficient.
statement 2: let 2v be the speed for first half, then v be the speed for second half.
d/2v + d/v = 4
d/4 = 2vsqure/3v
d/4 = 2/3 v.
as we don't know v. statement 2 is not sufficient.
combining st1 and 2. we can not calculate v. as 50 MPH given for first 2 hr and not first half of the journey.
Answer is E.
-------Analyze why option A in SC wrong-------