Найдите сумму первых восьми членов геометрической прогрессии -45 15 -5

There is a large table in my room. there are three windows in my classroom. there is a latter on your desk. there is a chair here. there is a table and two chairs in the room. there are flowers and a box of chocolates on the table. there are some books on my table. there are a lot of apples on the table. there are two shops and a cinema in my street. there is a blackboard, four desks and fve chairs in our class-room.

8х+7х=1500
15х=1500
х=1500:15
х=100

8*100=800 
7*100=700
800*700= 560000

25÷5=5
25÷5=5вот так будить я думаю

Ууптрпгеп3е7 это очень сложно, когда плюс 67