Jo has baked 40 cakes for her husband's 40th birthday, one for each of his years, weighing 1, 2, 3 40kg. she forgets which cake is which and has to check the weight of each cake using a large pair of balancing scales. each cake is placed individually on the left-hand pan of the scales and balanced againt one or more scale-weights which can be put on either or both scale pans as necessary. she has four scale-weights available, each a different whole number of kg. find their values in kg and make a list showing the particular combination of the scale-weights for identifying each cake