Answer:
There Are More Then One Way To Solve this Mathematical Problem .
4=12 [(4x4)-4=12]
6=30 [(6x6)-6=30]
7=42 [........ ]
9= [(9x9)-9=81-9= ?]
** n x(n-1) is also a way to solve this prob.
4x(4-1) = 12
..................
....................
9x (9-1)= ?