For (1) you can prove fairly easily that ABE and ACD are congruent triangles. From that, show that BDF and CEF are coongruent triangles.

For (2), of course, the sum of angles in any triangle is 180 degrees. I assume you already know that. For the rest, remember that and "exterior angle", such as b, is equal to the sum of the other two interior angles: b= x+ y, a= y+ z, and c= x+ z so a+ b+ c= (x+y)+ (y+z)+ (x+z)= 2x+ 2y+ 2z= 2(x+y+z).

For (c) show that triangle ABE is congruent to triangle ACD.