Observe the triangle figure and its angles are .

The sum of three angles in a triangle is .

Let the third angle in a triangle is .

So .

Group like terms.

Add 2 to each side.

Subtract 6x from each side.

Let the third angle in a triangle is .

The values is substitute in third angle .

The values is substitute in the first angle .

The values is substitute in the second angle .

Let the third angle in a triangle is and its angles are .