ANSWER
Find out the how long will the Yellow balloon be higher than the orange balloon.
To proof
Now the diagram is given below
As given
A yellow hot-air balloon is 100 feet off the ground and rising at rate of 8 feet per second.
i.e height of the yellow baloon off the ground = 100 feet
rising at rate = 8 feet per second.
.An orange hot-air balloon is 160 feet off the ground and rising at a rate of 5 feet per second.
i.e height of the orange baloon off the ground = 160 feet
rising at rate = 5feet per second.
Formula

Relative velocity = rising rate of yellow balloon - rising rate of orange balloon
= 8 -5
= 3 feet per second
Relative distance = height of the yellow baloon off the ground - height of the orange baloon off the ground
= 160 -100
= 60 feet
put in the formula

= 20 second
after 20 second Yellow balloon will be higher than the orange balloon.
Hence proved
Six million seven thousand two hundred
First, we count how far reached the Nell:
3,5 * 16 = 56 miles
Secondly, we count how far reached the Kristin:
3,5 * 18 = 63 miles
Now we expect the difference in the distance between them:
63 - 56 = 7 miles
The results that Kristin about seven miles driven more than Nell.