Well if there were three books that were all the same price and the sum was $40.20, you would simply divide the sum by three (amount of books). This is how the equation would look:
40.20/3= 13.40
Therefore, the price of one of the books is $13.40
The sail price would be 38.25 because the original price is 45 and the discount is 15% and that would be 0.15 you need to multiply 45 with 0.15 and that would 38.25
If there is 2 people and it costs 12 dollars you will first subtract 2 dolars for each person leaving you with 10 dollars. After that you will divide 10 by 2 for the miles because each mile costs 2 bucks. that will get you to 5 miles
