(bn)– арифметическая прогрессия. Найдите b4 , если b3=8 и b5=-4

1. Look! The ship (to float) across the Volga. 2. I am a chief designer, but I (not to work) now. I have a holiday. 3. What he (to read) now? 4. I met Kate when she (to walk) to the university. 5. My kids (not to do) their homework when I came home from work yesterday. 6. What you (to write) when the bell rang?7. Paul (to wait) for me outside the theater at this time tomorrow. 8. Pamela (not to sleep) the whole night tomorrow, as she is going to take part in the night performance. 9. Can you hear those people? What they (to talk) about? 10. What you (to talk) about when I entered the room? 
11. Hello, Pat! Where you (to go)? 12. Paul (to read) ‘The Financial Times’ now. 13. Nellie (to sort out) the letters which need immediate attention now. 14. We (to watch) a new film when the electricity went off. 15. What you (to do) when I met you yesterday?16. Paul (to have) a daily meeting with his deputy round about 9 tomorrow. 17. What you (to do) at 5 p.m. next Sunday? 18. Where is Mary? She (to type) her daily report. 19. We (not/to drive) fast when the accident took place. 20. Look! The puppies (to sleep).