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As shown in the figure, A, B, and C represent three circles with areas of 9, 10, and 11, respectively. It is known that the total area covered by the three circles is 20. The areas covered by the intersections of circles A & B, B & C, and C & A are 5, 4, and 3, respectively. Find the area covered by the intersection of all three circles A, B, and C.

Exploration:
We denote the total area covered by the three circles as A ∨ B ∨ C; the area covered by the intersections of any two circles as AB, BC, CA; the area covered by the intersection of all three circles as ABC. According to the problem:
(1) The sum of the areas of the three circles is: A + B + C = ______;
(2) The total overlapping area is (A + B + C) - A ∨ B ∨ C = ______;
(3) The sum of the areas covered by the intersections of any two circles is: AB + BC + CA = ______;
(4) The area covered by the intersection of all three circles: ABC = ______.
Summarize:
Utilize the above notation and solution process to complete the equation: ABC = ______.
Inspired by the method above, solve the following problem:
There are 74 students in a certain grade who participate in extracurricular groups. Of these, 34 participate in ball games, 32 participate in chess, and 30 participate in athletics. Seven participate in both ball games and chess, eight participate in both chess and athletics, and ten participate in both athletics and ball games. Find the number of students who participate in all three groups.