Answer:
∠CFD
Explanation:
You want to know the angles complementary to acute angle BFC in the given diagram.
Complementary angles
Angles are complementary when their sum is 90°. In general, only acute angles can be complementary.
In the given diagram, there are only two acute angles. One of them is ∠BFC. The other one is ∠CFD. Together, they total 90° angle BFD.
Angle CFD is complementary to angle BFC.