Suppose I bought x clothes.
(80-2)x= 1200
Obviously x is not an integer! So, your topic is wrong. According to the problem-setting model of Grade Three, it should be that after buying more than 10, the unit price of each additional piece is reduced by 2 yuan.
Suppose I bought x clothes.
[80-2(x- 10)]x= 1200
Solution: x? =20，x？ =30。
When x=20, the unit price = 80-2x (20-10) = 60;
When x=30, the unit price = 80-2x (30- 10) = 40.