15x+ 12( 10-x)= 3x+ 120≤ 130

X≤ 10/3

X is an integer.

x=0， 1，2，3

Answer: 0.1.2,3

B: 10, 9, 8, 7

(2) Set the total sewage discharge as W.

w = 250 x+220( 10-x)= 30x+2200≥2260

x≥2

The price increases with the increase of x.

Minimum X=2

The third kind

A: 2 B: 8

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