Math puzzle

Billy Boy

Oh, where have you been,
Billy Boy, Billy Boy?
Oh, where have you been,
Charming Billy?
I have been to seek a wife,
She's the joy of my life,
She's a young thing
And cannot leave her mother.

Did she bid you to come in,
Billy Boy, Billy Boy?
Did she bid you to come in,
Charming Billy?
Yes, she bade me to come in,
There's a dimple in her chin.
She's a young thing
And cannot leave her mother.