This question is asking "Where does cosine equal

?"
Based on our unit circle values and the domain of the cos^{-1} function, we see that at 30 degrees, or

, cosine is equal to

.
3(9+5n)
Use the distributive property to multiply 9 by 3 and 3 by 5n to get that answer.
The inequality is: x*0.75 + 3.00 < 20.00, where x represents the number of miles. When you solve the inequality, you get 22.66 miles. When you round up to 23 miles, you don't satisfy the inequality, so you have to round down to 22 miles.
Answer: (C) 22 miles