Question

1. (2n + 20)° (4n - 20)° n°

Explanation:

Step1: Recall angle - sum property of a triangle

The sum of the interior angles of a triangle is 180°. Also, an exterior angle of a triangle is equal to the sum of the two non - adjacent interior angles. Here, the exterior angle is $(4n - 20)^{\circ}$ and the two non - adjacent interior angles are $(2n + 20)^{\circ}$ and $n^{\circ}$. So, we can set up the equation $4n-20=(2n + 20)+n$.

Step2: Simplify the right - hand side of the equation

Combine like terms on the right - hand side: $(2n + 20)+n=3n + 20$. So the equation becomes $4n-20=3n + 20$.

Step3: Solve for n

Subtract $3n$ from both sides of the equation: $4n-3n-20=3n-3n + 20$, which simplifies to $n-20 = 20$. Then add 20 to both sides: $n-20 + 20=20 + 20$, so $n = 40$.

Answer:

$n = 40$