Which of the following expressions are polynomials in one variable and which are not $?$ State reason for your answer. If the given expression is a polynomial, state whether it is a polynomial in one variable or not

$x^{2}+x-3+\frac{4}{x}$

For the polynomial

$\frac{x^{3}+2 x+1}{5}-\frac{7}{2} x^{2}-x^{6},$ write

$(i)$ the degree of the polynomial

$(ii)$ the coefficient of $x^{3}$

$(iii)$ the coefficient of $x^{6}$

$(iv)$ the constant term

Factorise each of the following

$27 x^{3}-64-108 x^{2}+144 x$

Factorise

$x^{3}+12 x^{2}+39 x+28$

Without actually calculating the cubes, find the value of $48^{3}-30^{3}-18^{3}$