Construction: Extend ED, AB and CB.
∠BHF = ∠CBA
| Corresponding angles
∵ AB || FE and BH intersects them
= 75° ...(1)
∠BHF + ∠BHD = 180° | Linear pair axiom
⇒ 75° + ∠BHD = 180°
⇒ ∠BHD = 105° ...(2)
∠CDH + ∠CDE = 180° | Linear pair axiom
⇒ ∠CDH + 145° = 180°
⇒ ∠CDH = 35° ...(3)
In ∆CHD,
∠CDH + ∠CHD + ∠BCD = 180°
| Angle sum property of a triangle
⇒ 35° + 105° + ∠BCD = 180°
⇒ ∠BCD = 40°