Катер плывет против течения реки .Какова скорость катера относительно берега , если скорость катера относительно воды 4м/с , а скорость течения реки 3 м/с !!! Помогите пожалууустаааа

1. When I (to ring) up my friend, he (to sleep). 2. When grandfather (to watch) TV, he (to fall) asleep. 3. When my friend (to come) to see me, I (to do) my homework. 4. When I (to go) to the stadium, I (to meet) Kate and Ann. 5. When Nick (to ring) me up yesterday, I (to help) mother. 6. When the children (to walk) through the wood, they (to see) a fox. 7. When I (to come) home, my sister (to wash) the floor. 8. When Mike (to play) in the yard, he (to find) a ball. 9. When I (to draw) yesterday, I (to break) two pencils. 10. When I (to meet) Tom, he (to go) to the shop. 11. When I (to look) out of the window, the children (to play) hide-and-seek. 12. I (to go) to the theatre yesterday. 13. At seven o'clock yesterday I (to go) to the theatre. 14. What you (to do) at 5 o'clock yesterday? -I (to play) the piano. 15. When I (to come) to school, the children (to stand) near the classroom. 16. We (to play) in the yard the whole evening yesterday. 17. When I (to prepare) breakfast in the morning, I (to cut) my finger. 18. Last year I (to go) to the United States. 19. You (to go) to Great Britain last year? - No, I (to go) to France. 20. What you (to do) yesterday? — I (to translate) a very long article.