Using the Pythagorean Theorem we start by doing 4^2 x^2 = 5^2 8+x^2=25 -8+x^2 =25-8 x^2=17 take the square root of both sides and we get 4.12. So now we have all we need to find x now we continue 1^2 + x^2 =4.12^2 1+x^2=16.97 -1+x^2=16.97-1 x^2 =15.97 we take the square root of both sides to get 3.99 which is your final answer. Hope this helps! :D