Mot nen nha hinh chu nhat co chu vi 20m, chieu dai hon chieu rong la 2m. Nguoi ta lat nen nha bang cac vien gach vuong canh 2dm. Biet rang 12 vien gach nay gia 42 000 dong. Hoi nguoi ta da mua het bao nhieu tien gach lat nen ? (Dien tich phan manh vua khong dang ke).