Conditionally extract multiple values from field that are = to another field with a single value

[Adalberto_Santo]

Hello, i have a base with multiple tables, on my main table i have a field which represents the days old the animal is, on another field i have a rollup which gives me multiple values of the days that the animal brothers were born. I am trying to figure out how to count values that are the same on both fields so that i can know if the original animal was born as a single, twin or triplet, but i have not figured out a formula or a way to do this.
Any help would be aprpreciated.
Thanks in advance
Here is part of the table to help understand, the Type of Birth is the field that has the incorrect formula