text: Your phrasing makes the question unclear (what goes where?) so I'll just go through the different possibilities.  One is this:\n\n\nsq(5x)*sq(x-4)*sq(5)\n\nYou can multiply together things in square roots.  Let's do this:\n\nsq(5(5x)(x-4)=\nsq(25x(x-4))=\nsq(25x^2-100x)\n\n\nAnother possibility is this:\n\nsq(5x)*sq(x)-4sq(5)=\n\nBring the x out of sq(5x), by making it sq(x) (because you can take out things that are multiplied in square roots, but make sure they are still under a square root sign!)\n\nsq(5)*sq(x)*sq(x)-4sq(5).\n\nsq(x)*sq(x)=x.  We are multiply two square roots, so bring the x's under the same one.  Multiply them, we get x^2.  The square root of x^2 is x.\n\nx(sq(5))-4sq(5)=sq(5)(x-4)\n\nThere's your answer, if that was indeed the way I should have interpreted the question.\n\nHope this helps.