If interior angle is ∡B=120° - obtuse angle then exterior angle ∡B1=60°
In the obtuse triangle height hB is out of the triangle.
We can calculate height hB in this way sin °60= hB/BC => hB= BC * sin 60°
hB= 10 * √3/2= 5√3
Formula for the area of the triangle is A= AB*hB/2= 6*5√3/2=15√3
A=15√3
Good luck!!!
