Знайти суму перших пятнадцяти членів арифметичної прогресії, у якій перший член дорівнює 7, а пятнадцятий дорівнює 83

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.

i don't want to answer the teacher's questions.

my friends and i  go to school every day.

i do my homework at school.

every friday the students tidy their classrooms.

we don't have to wear a uniform  at our school.

as a rule they  come to school at 8 a.m.

my sister like to make reports on geography.

we must do washing up every day.

i have to play chess two times a week.

we go to a swimming pool three times a week.

my mother goes to the dentist two times a month.

i go to the disco three times a month.

i have never been to volgograd.

she goes to the cinema very often.

they seldom sing and dance.