If `""^(n)P_(4)=1680,` find n.

If ""^(n)P_(4)=210 , find n.

If ""^(n-1)P_(3): ""^(n)P_(4)=1:9 find n.

If ""^((n-1))P_(3):""^(n)P_(4)=1:10 , find n.

If ^(n)P_(4)=360, find the value of n

(i) If ""^(n)P_(4): ""^(n)P_(5)=1:2 , find n. (ii) If ""^(n-1)P_(3): ""^(n+1)P_(3)=5:12 , find n.

If a,b,c are the values of n where ""^(n)P _(7) = 42 ""^(n)P_(5) ,""^(n)P_(4) = 1680 , ""^(n) P_(3) =1320 respectively then the ascending order of a,b,c is