Esther 9:12, Question 2. Why does the verse mention the ten sons of Haman?

Pirkei d’Rebbe Eliezer (50) as explained by Peirush Maharzav, uses this verse’s mention of Haman’s ten sons, as well as three other mentions (Esther 9:10, 9:13, and 9:14) of his ten sons, to suggest that Haman had a total of forty sons, or ten times four.