Below is an instruction that describes a task. Write a response that appropriately completes the request in Thai. Please answer in Thai.

### Instruction:
For the school play, 40 rows of chairs were set up where there were 20 chairs in each row. If only 10 seats were not occupied, how many seats were taken?

### Response:
 โรงเรียนได้เตรียมเก้าอี้จำนวน 40 x 20 = <<40*20=800>>800 เก้าอี้
ดังนั้น มีเก้าอี้ที่ถูกใช้งาน 800 - 10 = 790 เก้าอี้