What must be added to the following expression to make it a perfect square.

$25x^2-70x+7$

What must be added to the following expression to make it a perfect square.

$4x^2-60x+15$

Simplify:

$\left(x+1\right)\left(x-1\right)\left(x^2+1\right)\left(x^4+1\right)$

Simplify:

$\left(3x-4y\right)\left(3x+4y\right)\left(9x^2+16y^2\right)$

Simplify:

$\left(x-\frac{1}{x}\right)\left(x+\frac{1}{x}\right)\left(x^2+\frac{1}{x^2}\right)$

Find the greatest common factor of the following monomials:

$3abc$ and $9xyz$

Find the greatest common factor of the following monomials:

$x^{2}y$ and $2xy$

Find the greatest common factor of the following monomials:

$2lmn$ and $4lpq$

Find the greatest common factor of the following monomials:

$he$ and $she$