Answer:
90°, and it's a right angle.
Explanation:
Reading a protractor is a lot like reading a number line.
Most often you'd be reading an angle like AOC (25°) or AOD (115°).
And you can still do that here.
But now recognize that COD is just AOD with AOC cut off. Do you see it? Then it's just a subtraction problem:
COD = AOD - AOC = 115 - 25 = 90°
How do you classify a 90° angle? Is it acute or obtuse? No, it's a right angle.
Alternate Method:
I started out talking about number lines because that's how I first saw the problem, then talked myself into the above answer.
But look at ray OC where it crosses the "number line" or the angle rule: doesn't it cross at 25? And ray OD crosses at 115. And just like on a number line, you can find the difference between those two numbers. That's 90, which is the angle of COD.