Знайти різницю арифметичної прогресії, якщо S11 = 561 i a9 = 84.​

at our lessons we answer the teacher's questions.

in england they don't go to school every day.

i do my homework in my bedroom.

the pupils on duty tidy the classroom.

all the pupils have to wear uniforms.

i come to school at a quarter to eight.

we like to make reports.

 

i do me homework every day.

i have my music lessons two times a week.

we have english three times a week.

this magazine is published to times a month.

i visit my aunt three times a month.

i never miss classes.

i go to the forest very often.

they seldom go to the theatre.