The coefficient of $x^n$ in the expansion of $\frac{1-a x-x^2}{e^x}$ is

For three numbers $a, b, c$ between 2 and 18 such that their sum is 25 , the numbers $2, a, b$ are in AP and the numbers $b, c, 18$ are in GP Then, the value of $a+b+c$ is

If $a, b, c, d$ be four positive unequal quantities and $s=a+b+c+d$, then $(s-a)(s-b)(s-c) (s-d)>k a b c d$. Then, value of $k$ is

If $ a > 0, b > 0, c > 0 $ and $ a, b, c $ are distinct, then $ (a+b)(b+c)(c+a) $ is greater than