Answer:
M<C = 37 degrees
M<D = 86 degrees
M<DEC = 111 degrees
Explanation:
The exterior angle theorem can be measured by the hypotenuse of a 90 degree angle. Since there is no hypotenuse in the matrix, you don't need to make it positive :)
Therefore, after using this theorem, I came to the conclusion that m/C would be 37 degrees, since I calculated the measure of the angle. I used the same tactic on m/D and m/DEC.
I hope this helps :)