2. The ordinate y represents the total amount of money in the hands of farmers.
It is not difficult to see that when selling 0kg potatoes, the money in hand is 5 yuan, while when selling potatoes,
At 30kg, it was 20 yuan, that is, 20-5= 15 yuan, 15/30=0.5 yuan/kg. After the price reduction, the remaining potatoes are sold out in 0.4 yuan and sold in 6 yuan, that is, 6/0.4= 15kg potatoes are sold.
To sum up:
(1) The change brought by farmers is 5 yuan.
(2) Before the price reduction, the price of potatoes per kilogram was 0.5 yuan per kilogram.
He brought 45 kilograms of potatoes.