Hi,
During one cycle of oogenesis, 3 polar bodies are formed. Since the question is asking about 10 years (= 120 months) in which 2 babies took births (9 months *2= 18 months) during which no oogenesis occurs.
So, 120-18 = 102 months
Every month, 3 polar bodies forms. Hence 102*3 = 306 polar bodies.