D = ABC + ABC + ABC
+ ABC + ABC + ABC + ABC
E = A + AB + ABC
F = A + AB + ABC
D = ABC + ABC + ABC + ABC + ABC + ABC + ABC
E = ABC + ABC + ABC + ABC + ABC + ABC + ABC
F = ABC + ABC + ABC + ABC + ABC + ABC + ABC
(We noticed that E is always 1 when A is 1 (as well as 3 other times) and that F is always 1 when A is 0 (as well as 3 other times.)
D = ABC + ABC + ABC
+ ABC + ABC + ABC + ABC
E = A + AB + ABC
F = A + AB + ABC
(We've gone from 24 gates to 12.)
D = A + AB + ABC
E = A + AB + ABC
F = A + AB + ABC
(Now we've gone to 9 gates, but algebraic simplification of boolean expressions isn't always easy.)