one would have to believe since there is only 3 angles, it is a triangle which has a total of 180 degrees. They give us the degrees for all the angles, we just have to add them up and solve for x.
180° = ∠A + ∠B + ∠C
180° = 65° + (3X-10)° + 2X° Drop the parentheses
180° = 65 + 3x - 10 + 2x Combine like terms
180° = 55 + 5x subtract 55 from both sides
125° = 5x divide both sides by 5
25° = x substitute this value for x into the ∠'s
∠A = 65°
∠B = 3x - 10
= 3(25) - 10
= 65°
∠C = 2x
= 2(25)
= 50°