plz post your attempt at the question, without which the purpose of forum is defeated. also can you attach the circuit diagram because its not quite clear to
me.
well, i dont remember solving unbalanced load question, but somewhere i read
that power for each phase remains constant so may be 3.5/3 kva per phase, i m not sure if it applies to unbalanced situation so please check if that is the case. if it is then voltage calculation becomes easy .will get back to you if i get a some clue.
for solving problems based on unbalanced load the method of symmetrical components is used. (i myself m working on it now thanks to you ).