Then ∠C+∠D=∠CTE,
And ∠CTE+∠E=∠BMF.
That is ∠C+∠D+∠E=∠BMF.
rule
Angle A+ angle ABC+ angle C+ angle D+ angle DEF+ angle F.
= Angle A+ Angle ABC+ Angle BMF+ Angle F (these four angles are the quadrilateral of ABMF)
=(4-2)× 180
=360