Question

multiply and simplify if possible.
sqrt 5x(sqrt x-5 sqrt 5)

Answer 1

Making the assumption that your problem looks like this,
$\sqrt{5x}(\sqrt{x}-5\sqrt{5})$

we use the distributive property to multiply:
$\sqrt{5x}\times \sqrt{x}-\sqrt{5x}\times5\sqrt{5} \\ \\ \sqrt{5x^2} - 5\sqrt{25x} \\ \\ x\sqrt{5}-25\sqrt{x}$