Answer:
∠ ECF = 75°
Explanation:
the central angle of a circle is equal to the arc that subtends it, then
DE = 30x - 1
the sum of the arcs in a circle = 360° , that is
FD + DE + EF = 360° , so
28x - 4 + 30x - 1 + 15x = 360
73x - 5 = 360 ( add 5 to both sides )
73x = 365 ( divide both sides by 73 )
x = 5
then
EF = 15x = 15(5) = 75°
and so ∠ ECF = 75°