I believe the answer you are looking for is "repitieron". Since it is the past tense verb for "they or ellos".
Answer:
professora, sus pantalones son bonitos
You must keep in mind that nouns must match gender and number. In this case both Laura and Virginia are female and there are two of them. This means that the nouns will end in -as (-a for females and -s for plural)
Laura y Virginia son bajas y delgadas
Hope this helped!
~Just a girl in love with Shawn Mendes