Mark M. answered 02/16/21
Retired Math prof with teaching and tutoring experience in trig.
Since 3 sides are given, use the Law of Cosines to find the largest angle (which is opposite the longest side) first
Find β: b2 = a2 + c2 - 2accosβ
196 = 100 + 144 - 2(10)(12)cosβ
196 = 244 - 240cosβ
cosβ = 0.2
β = Cos-1(0.2) = 78°
Now, use the Law of Sines to find one of the other angles and then use the fact that the 3 angle measures add up to 180° to get the remaining angle.