Question 473539
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To isolate n you need to multiply everything out, then simplify by adding like terms
You should end up with a 4th degree polynomial:
{{{n^4 - 2n^3 - 19n^2 - 28n - 12 = 0}}}
Now n must be a positive integer because we are dealing with a permutation.
Use synthetic division to try to factor out a factor of 12.
Try 1,2,3,4,6,12 these are the only possible solutions.
If you get a zero remainder then its the solution.