[tex]\huge\underline{\underline{\boxed{\mathbb {SOLUTION:}}}}[/tex]
Given:
▪ [tex]\longrightarrow \sf{KED = 100^\circ}[/tex]
▪ [tex]\longrightarrow \sf{\angle ECD = 60^\circ}[/tex]
[tex]\leadsto[/tex] According to the triangle angle sum theorem, the sum of interior angles of a triangle is 180°.
[tex]\leadsto[/tex] We can find the value of ∠E if we know the sum of two supplementary angles is equal to 180°
[tex]\longrightarrow \sf{m \angle E+ m \angle K=180^\circ}[/tex]
[tex]\longrightarrow \sf{m \angle E+ 100^\circ =180^\circ}[/tex]
[tex]\longrightarrow \sf{m \angle E= 80^\circ}[/tex]
As we find the value of ∠E, we can replace it in the initial formula. [tex]\downarrow[/tex]
[tex]\huge\underline{\underline{\boxed{\mathbb {ANSWER:}}}}[/tex]
[tex]\bm{m \angle C + m \angle \boxed{\bm D} = m \angle \boxed{\bm E}}[/tex]
[tex]\bm{m \angle D= \boxed{\bm{ 40^\circ}}}[/tex]
