The general rule of thumb is this: the largest angle is always opposite the largest side of the triangle.
We see that AB = 3.8 is the largest side, meaning that angle C is the largest angle which is opposite of AB. We don't need to actually find the value of angle C. Though optionally you can use the law of cosines to do so (and compare with the values for angles A & B to help confirm the answer).
note: a similar rule is that the smallest side is always opposite the smallest angle. The smallest angle in this case is angle B. The order of the angles from smallest to largest is B, A, C.
