Petra was preparing for a long trip, and filled her gas tank up with 45
litres of gas the night before she left. She noticed that her odometer read 21 912
km when she left the gas station. During the trip she filled up her tank with 35.45
L on her first stop, then with 30.5 L on her second stop, and finally filled the tank
at the end of her trip with 30 L of gas. The odometer on her car read the last
palindromic number in the twenty-two thousands. What was the average number
of litres per 100 km used by Petra's car during the trip?