The value of x using the exterior angle theorem is 22.
To find the value of x,
Given the exterior angle theorem which states that the measure of an exterior angle is equal to the sum of the measures of the two opposite(remote) interior angles of the triangle.
Given ∠A + ∠B = 123°(Exterior angle)
So, 2x + 8 + 3x + 5 = 123°
5x + 13 = 123°
5x = 123 - 13
5x = 110
divide through by 5
5x/5 = 110/5
x = 22
Therefore , the value of x using the exterior angle theorem is 22