A is X bottle, and B is (100-x) bottle.

So: 20x+30 (100-x) < = 2800->; x & gt=20

30x+20( 100-x)& lt； = 2800->； x & lt=80

So 20

2. According to the meaning, y=2.6x+2.8( 100-x).

= 100-0.2x

It is a monotonic decreasing function, so the minimum value is taken at the maximum value of x,

According to 1, the maximum value of x is 80, so the minimum cost is:

100-0.2× 80 =100-16 = 84 (yuan)