Use the given minimum and maximum data entries, and the number of classes, to find the class width, the lower class limits, and the upper class limits. minimum $=12$, maximum $=73,7$ classes

Step 1 ：Given the minimum value as 12, the maximum value as 73 and the number of classes as 7.

Step 2 ：Calculate the class width by subtracting the minimum value from the maximum value and then dividing by the number of classes. This gives us \(\frac{73-12}{7} = 9\).

Step 3 ：Find the lower class limits by adding the class width times the class number to the minimum value. This gives us the list [12, 21, 30, 39, 48, 57, 66].

Step 4 ：Find the upper class limits by adding the class width to the lower class limit. This gives us the list [21, 30, 39, 48, 57, 66, 75].

Step 5 ：Final Answer: The class width is \(\boxed{9}\). The lower class limits are \(\boxed{12, 21, 30, 39, 48, 57, 66}\). The upper class limits are \(\boxed{21, 30, 39, 48, 57, 66, 75}\).