1 How have you solved this difficult math question
-> How has this difficult math question been solved?
2 she hasn’t prepared for dinner since 6.30pm
-> Dinner hasn't been prepared by her since 6.30pm
3 The company has hired new workers
-> New workers have been hired by the company
4 Have the thieves stolen the most valuable painting in the national museum?
-> Has the most valuable painting in the national museum been stolen by the thieves?
5. Have you finished the above sentences ?
-> Have the above sentences been finished?
6. have you sent the Christmas cards to your family?
-> Have the Christmas cards been sent to your family?