Answer:
10 cm long
Explanation:
Since a rhombus has all equal sides, therefore each side is 10 cm long, so each opposite is equal to each other and as well as corresponding sides equal, it would work for a square as well but each angle has to be 90* but is 30* and all angles have to add up to 360*, and opposite angles are congruent so it is 30* on the other side, and the other ones would be 150* since it has to add up to 360*, but each side is equal to 10 cm.