The number of all species in which 4 out of 7 people spoke-the number of species in which both parties did not participate-the number of adjacent species in which both parties participated.

=7*6*5*4-5*4*3*2-2*3*5*4

=840- 120- 120

=600

Four of the seven people were chosen to speak. Various: 7*6*5*4. Should be ok?

Number of species that neither Party A nor Party B participates in: 5*4*3*2, which is the arrangement of 4 out of 5.

Number of adjacent species involved by Party A and Party B: 2*3*5*4. With the binding method, Party A and Party B are regarded as one person first, 2 means that Party A and Party B can be transposed in two ways, 3 means that when Party A and Party B are regarded as one person, they are regarded as three people, and 5 and 4 mean the selection methods of the third and fourth people.

Do you understand?