Задачі на прогресії/2

$$

1) a_5+a_6 = 31, a = 1, d - ?

2) a_3+a_9 = 15, a = 7, d - ?

3) a_11= 28, a_1 = 6, d - ?

4) a=3, d= 5, a_{30}, a_{44}

5) a_9 - a_3 = 12, a - ? d - ?

$$