Explanation:
Estoy. As "I am okay" or "content." Estar means"to be". So since it's in the Yo form it's estoy.
Just in case you need other forms of Estar
Yo-Estoy
Tu-Estás
El Ella Usted-Está
Nosotros-Estamos
Ellos Ellas Ustedes-Estan
nosotros: we
estar: to be
alegrar: to cheer upto make happy
or
nosotros: we
ser: to be
alegrar: to cheer upto make happy