So this gives us a few clues. The numbers all have an equal value between them, and the fourth and fifth are 27 and 32 respectively. So how much is between these two?
5, so since you add five to go from fourth to fifth, you subtract to go backwards. So then the third is 27-5 = 22 and so on, can you figure it out from there? just subtract 5 however many more times is needed.
We are dividing the parking amount they had to pay by the 5 friends since they are splitting the amount they pay. Then we are adding 30 because that is how much each friend is paying.