When do we use exterior angle property and angle sum property ? Explain the differance please hurry!!!!!!!!!

Exterior angle property is used when one side of a triangle is extended as given in the figure above.

Therefore, if ∠1 and ∠ 2 are given you can find the value of ∠4 by using exterior angle property.

Angle sum property is used when two angles of a triangle are given and we are supposed to find the third angle. For example if ∠1 and ∠3 are given we can find ∠2 by using angle sum property.