All the angles in a circle equal to 360 degrees. So basically just add up all the known values: 23+23+15=61 and then subtract that from 360: 360-61=299.
You can also do 23+23+15+x=360. Adding it all becomes 61+x=360, subtract 61 from both sides of the equation, and you get x=299.
(Something to help remember is that the angle is obtuse, meaning it’s automatically more than 90 degrees, hope this helps!)
The rule for 90 degree clockwise rotation is (x,y) turns into (y,-x) therefore if you use your numbers (2,-6) and then use the 90 degree clockwise rotation rule it becomes (-6,-2)
