#### Answer

The proof is in the following form:
Column 1 of proof; Column 2 of proof.
Thus, we have:
1. ABCD is a parallelogram, and DB intersects AE at point F; given
2. Angle ADC is congruent to angle CBA; opposite angles of parallelograms are congruent.
3. EDF is congruent to ABF; from (2) and the fact that DB cuts the two angles the same way on both sides, it follows that the two are congruent.
4. AFB is congruent to DFE; vertical angles theorem
5. DFE is similar to AFB; AA similarity theorem
6. $\frac{AF}{EF} = \frac{AB}{DE}$; CPSSTP