If $m$ and $M$ are respectively, the smallest and greatest rational roots of the equation $6 x^6-25 x^5+31 x^4-31 x^2+25 x-6=0$, then $M-m=$

The number of ways of arranging the letters of the word LINEAR so that the letters N and R do not come together and E and A come together is

15 lines are concurrent at a point $P$. A line $L$ is not passing through $P$ intersects all the 15 lines and forms triangles with them. Then, the number of triangles having $L$ as one of its side is

The expansion of $(a+x)^n$ contains 15 terms. When $x=1$ the ratio of the neighbouring terms to the middle term in this expansion is 16 . Then, the positive integral value of ' $a$ ' is