12x + 10 (10-x) ≤ 105, the solution x ≤ 2.5.
∵ x to take a non-negative integer, ∴ x can be taken as 0, 1, 2.
There are three kinds of purchasing program: purchase of A-type 0, B-type 10 units;
A-type 1, B-type 9 units;
A-type 2, B-type 8 units.
(2) 240x + 200 (10 - x) ≥ 2040,
Solve x ≥ 1, so x is 1 or 2.
When x = 1, the purchase of funds for: 12 × 1 + 10 × 9 = 1.02 (million yuan);
When x = 2, the purchase of funds for 12 × 2 + 10 × 8 = 1.04 (million yuan),
So in order to save money, should buy A type 1 units, B type 9 units.
(3) 10 years the total funds of the enterprise's own sewage treatment:
102 + 10 × 10 = 2.02 (million yuan),
If the sewage will be discharged to the sewage plant to treat:
2040 × 12 × 10 × 10 = 2,448,000 (yuan) = 2,448,000 (million yuan).
Saving money: 244.8-202 = 42.8 (yuan).