Implement count method - Usage of class variable & instance variable

vehicle.rb

class Vehicle
end

class Car < Vehicle
end

class Bus < Vehicle
end

class Jeep < Vehicle
end


Jeep.new(name: 'Compass')
Bus.new(name: 'Airavat')
Car.new(name: 'Wagon R')

# implement Vehicle.count and it should return 3 in the above case.

Vehicle.count