2,6 is set by the player's X rule (x+ 1)*x/2=2 1, and the result is x=6.
The titles of the third and fourth questions are unclear.
5. 100 or let the original price be x, then x*0.9* 1. 1=99, and the solution is x= 100.
6,614 I don't know if I understand your topic correctly. ...
Judging from the problem, 7-m-7x=x+ 1
M=6-8x Because X is not equal to 0 or-1, M is not equal to 6 or 14.