1)if you have time write a letter to your friends
2)with the case if the weather is good we will swim and sunbathe3)if you go by train you better buy tickets in advance
4)if you stay with us for another two days, I will show you all the landmarks of Petersburg
5)I will write to you if there is time
6)I would call him if I were you and ask about his health
7)he would have done his homework yesterday if he had not been so busy