You can use Soh Cah Toa to get your answer, in other words, sin cos tan. If you already have x, that means you probably used tan, which is adjacent and opposite. Now for y, you are trying to find the hypotenuse so you could use, sin or cos, for sin you would use the adjacent (x) and the hypotenuse (y) and for cos, you would use opposite (4) and the hypotenuse (y). This is all based on the angle 45.