Which of the following expressions is a polynomial, state the reason ? If an expression is polynomial, state whether it is a polynomial in one variable or not

$3 x^{2}+5 x-7+\frac{8}{x}$

Expand

$(3 x+5)^{2}$

Without actually calculating the cubes, find the value of each of the following

$(31)^{3}-(16)^{3}-(15)^{3}$

From the following polynomials find out which of them has $(x+1)$ as a factor

$x^{3}-5 x^{2}+2 x+8$

Find $p(1), p(2)$ and $p(4)$ for each of the following polynomials

$p(x)=x^{3}-7 x^{2}+14 x-8$

Find the value of each of the following polynomials at the indicated value of variables

$p(t)=5 t^{2}-11 t+7$ at $t=a$