Hello!
To start, since you already know that you can drive 3000 miles in 75 hours, but you need to know how long it will take to drive 4000 miles, you can solve using a proportion, where x is the amount of hours:
3000/75=4000/x
When you have set this up, cross multiply:
3000*x=75*4000
After you have cross multiplied, you will result in this:
3000x=300000
Then, solve for x and you will get x=100, meaning it will take Cheyenne 100 hours to drive 4000 miles.