Question

if angle ABF=100 and angle DCE=65

Answer 1

angle ABC is 180-100= 80
and angle ABC is 180-80+65=35

Answer 2

angle acb= 65 ( vertically opp angle )
angle fba +abc=180 ( linear pair )
100+abc=180
abc=180-100
abc =80
abc+bac+acb=180 (angle sum property )
80+bac+65=180
bac=35