Earnings in the third year

The average annual profit of A is y = (50x-98-12x-4 (x2-x)/2)/x.

Y= 12 Li 26+ 12 * 7 = 165438+ ten thousand yuan.

B total income y = (50x-98- 12x-4 (x 2-x)/2)

That is, when X= 10, the profit is 8+51*10 = 5180,000 yuan.

B cost-effective.