Answer:
The angle supplementary to ∠AFB is ∠EFA.
The reason why this is, is because a supplementary angle consists of two angles that have a sum of 180°.
Supplementary angles combine to form a straight line.
In this case, ∠EFA is the supplement of ∠AFB because, ∠EFA is the other part of the angle, AFB, that creates a full straight line(180°).
And to find the value of m∠EFA you would need to arrange an equation.
Since we know that the given angle measure of AFB is 78°, ∠EFA would have to equal a different measure so that both measures will have a sum of 180°.
We will consider the value of m∠EFA to be 'x' in our equation, so;
x + 78 = 180°
Solve for x:-
-78 -78
x = 102°, therefore m∠EFA = 102°.