SOLUTION: 2n! divided by (n-3)! = 84n

The left side is a factorial.
For the right side to be a factorial beginning
with 7*6, it must be 7! or 7*6*5*4*3*2*1.
Then (n-3)! must be 5*4*3*2*1 or 5!

Therefore







Checking:











So it checks:

Solution: 

Edwin