<u><em>Answer:</em></u>
The answer is 15 degrees.
<u><em>Step-by-step explanation:</em></u>
1) Do you see the little square symbol at the bottom right corner? That represents that the angle is a <u>right</u> angle, or a <u>90 degree</u> angle, in other words.
2) If you know that the first part of the angle is 45 degrees, as it is already labeled, then subtract 90 degrees - 45 degrees = 45 degrees, which is the angle that is left.
3) Set 3x equal to 45 degrees, and solve.
4) So, the equation is 3x = 45; divide by 3 on both sides to get x = 15 degrees.
Hope this helps! Feel free to give me Brainliest if you feel this helped. Have a good day, and good luck on your assignment. :)