Explanation:
come on, common sense (really read the options !) :
2. a singer ACCOMPANIED by a guitar ...
SOLO WITH ACCOMPANIMENT
3. singing Manang Biday in Acapella (correctly "a cappella" or "a capella". this means nowadays "singing without instrumental accompaniment".
this depends now : is there only one person singing, or a group ? my guess is based on the phrasing that only "you" is singing (one person).
SOLO
4. grade 6 learners singing "are you sleeping" IN ROUND.
DUET, PARTNER SONG, IN ROUND
5. Christian Bautista singing "way you look at me" with piano ACCOMPANIMENT
SOLO WITH ACCOMPANIMENT
6. Sarah and Leah singing "a while new world" TOGETHER. so, they are 2 people singing together. that is the meaning of a Duet.
DUET, PARTNER SONG, IN ROUND