Question

what is ( mangle f )?
( mangle f = square^circ )

Explanation:

Step1: Identify right angle in circle

$\angle EDF = 90^\circ$ (angle inscribed in a semicircle)

Step2: Calculate $\angle F$ via triangle sum

The sum of angles in $\triangle EDF$ is $180^\circ$.
$m\angle F = 180^\circ - 90^\circ - 60^\circ$

Answer:

$30$