Change the sentences from the active to the passive

Ex1 Change the sentences from the active to the passive    
1. The students were writing the lessons
   2 people will build this building next year
   3 He didn t type the leeter last night
   4 He is writing a new book .
5 My father hasn t found his keys yet
   6 He will solve the problem soon
   7 My father is washing the cat
   8 we were painting the gate
  9 I have eaten a hamburger .
10 I have opened the present
   11 The students are going to plant trees here
   12 My mother is going to sell this house
13 Tom delivers the mail every day
14 The teacher corrects out exercises
15 No one believes his stor