78×.33=25.74 busses are new
25.74+15=40.74 new busses
78+15=93 total busses
40.74/78=0.5223076923= 52% will be new with the new 15 busses
Answer:
0.5hrs
Step-by-step explanation:
Let the speed downhill be
,
Speed uphill is
. We are told than speed uphill is
the speed on flat ground. Therefore the speed on level ground will be
.
From this info, we can obtain the actual speed,
on level ground as:

speed, distance and time have the relation
so to obtain time to cover 45miles:

Hence it takes 0.5hrs to cover 45miles on flat ground.