Evaluate the expression if a = 6 and b = 3 3(a + 2b)

The complete question in the attached figure

we know that

 angle < DEF is an inscribed angle.
An inscribed angle is an angle with its vertex on the circle which is formed by two intersecting chords.
The inscribed angle measures half of the arc it comprises
the arc it comprises is the arc DCF

 the arc DCF is equal to (360°-248°) > 112°.

Hence ∡DEF is equal to  arc DCF/2> 112°/2> 56°

the answer is
∡DEF=56°