Because it is obtuse, the maximum is only 179 degrees.

Assuming that both angles are 179 degrees, then1/6 (α+β) =1/6 (179+179) =1/6 (358). ...

So 1/6 (α+β) cannot be greater than 59.6...6, which excludes C and D.

Substitute a into the formula and you get

Multiply 26 by 6= 156 and divide by 2 to get 78.

And 78 is less than 9 1, so a is also wrong.

So b is right.