Arccosine is the same as inverse cosine. On your calculator there should be a button labeled
Make sure your calculator is in degree mode
The decimal result for y, shown above, is approximate. I rounded to two decimal places to show the final answer. Round however you need to if your teacher instructs otherwise.
The angle made by any right angle is 90° and the angle made by a straight line is 180°. These are the main equations required to solve the values of x. The first 2 are right angles and the last 2 are straight lines. So the sum of the components within that right angle is 90° and for a straight line is 180°.