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nP6 = n*(n-1)*(n-2)*(n-3)*(n-4)*(n-5) (6 factors).
nP5 = n*(n-1)*(n-2)*(n-3)*(n-4) (5 factors)
The condition gives you this equation
n*(n-1)*(n-2)*(n-3)*(n-4)*(n-5) = 3 * n*(n-1)*(n-2)*(n-3)*(n-4).
Cancel n*(n-1)*(n-2)*(n-3)*(n-4) in both sides.
You will get
n-5 = 3.
Answer. n = 8.