7x+3(40？ x)≤2404x+6(40？ x)≤ 196

Solution: 22≤x≤30,

Because X is an integer, X takes 22, 23, 24, 25, 26, 27, 28, 29, 30.

So there are nine ways;

(2) The total assembly cost y=20x+ 18(40-x)=2x+720,

∫k = 2 > 0，

Y increases with the increase of x,

When x=22, the total assembly cost is the least, and the minimum assembly cost is 2×22+720=764 yuan.

The assembly scheme with the lowest total assembly cost is to assemble 22 A-type equipment and 18 B-type equipment.