On a bus, the ratio of the number of adults to the number of children was 4 : 5. After 6 children alighted and 6 adults boarded the bus, the ratio of the number of adults to the number of children became 7 : 2. <hr>There were <input min="0" type="number" id ="imp5pg101q9_1" class="lineinput" placeholder="?" /> passengers on the bus in the end.