15. If X Class A workers are recruited, then Class B workers are recruited (150-x).

According to the meaning of the question, 150-x≥2x, and x≤50 is the solution.

If the monthly salary is Y yuan, then Y = 600 x+1000 (150-x) =-400 x+150000.

The coefficient of ∵x is -400 < 0, and ∴y decreases with the increase of x 。

When x is equal to 50, y (minimum value) =-400× 50+150000 =130000 (yuan).

Therefore, the monthly salary of 50 A-type workers can be at least130,000 yuan.

16.c (hint: 20% < 30x15%+50x ÷ 80 < 35%)

17.( 1)x satisfies the inequality group {9x+4 (50-x) ≤ 360,

3x+ 10(50-x)≤290。

(2) There are three production schemes: 30 pieces of product A and 20 pieces of product B; Produce 3 1 piece of a product and 0/9/piece of b product; 32 A-type basic products and 18 B-type products were produced.

Finally, it's done. This is my first time typing! Add more! ! ! !