Final answer:
Angle a in parallelogram ABCD is congruent to the measure of angle f in parallelogram EFGH.
Step-by-step explanation:
To determine the measure of angle ___ that is congruent to angle a, we need to understand that corresponding angles in similar figures are congruent. Since parallelogram ABCD is similar to parallelogram EFGH, angle a in ABCD corresponds to angle f in EFGH. Therefore, angle a is congruent to the measure of angle f.