According to the Exterior Angle Theorem, the measure of an exterior angle of a triangle is equal to the sum of the measures of the two nonadjacent interior angles. Let's write an equation applying this theorem.
9x+9=45+5x
We will now solve the above equation for x.
Once we know the value of x=9, we can substitute it to the expression of the exterior angle.
9x+9 → 9( 9)+9 → 90
Therefore, the measure of the exterior angle is 90^(∘).
