A shopkeeper bought a total of 20 bags of grains having an average weight of 60.5 kg per bag. Out of these, the average weight of the 7 rice bags was 60 kg per bag, while the average weight of a wheat bag was 4 kg more than that of a maize bag. If 9 of the bags contained wheat while the remaining contained maize, what is the average weight of a maize bag?