Bonjour,
Réponse :
a. It's Alice's handbag. It's her bag.
( C'est le sac d'Alice. C'est son sac )
her = possesseur féminin
b. It's Luke's trampoline. It's his trampoline.
( C'est le trampoline de Like. C'est son trampoline )
his = possesseur masculin
c. It's Alex's and my family. It's our family.
( C'est Alex et ma famille. C'est notre famille )
d. It's Claire and Phil's bedroom. It's their bedroom.
( C'est la chambre de Claire et Phil. C'est leur chambre )
e. It's a present from Dad. It's my phone.
( C'est un cadeau de papa. C'est mon téléphone )
f. You did this, Alice. It's your problem!
( Tu as fais ça, Alice. C'est ton problème )