The exercise gives us the information that wheat producers will supply a different amount at each price level.
In economic theory, the supply and demand for a good are adjustable by its price. For example, if price goes up, more producers will offer wheat, but consumers will buy less. With the fall in demand, the price of wheat also lowers.
The same reasoning can be used when increasing the cost of production leads to a decrease in the price of wheat. Demand will adjust to price. As there will be different levels of price, demand behavior will also be varied, up to balance.
For example, the producer initially offered 100kg of wheat at a price of $ 10. If the cost of production has increased, the producer will have two options: to increase the price or to reduce the supply. In the exercise, he prefers to decrease supply. Let's assume that the offer falls to 30kg at a price of $ 10. There will be a choked demand needing wheat.
Thus, with each price increase the producer will offer more. Using hypothetical examples:
If he charges $ 12, he can increase the offer to 60kg
If you charge $ 15,he can increase the offer to 120kg
If you charge $ 50,he can increase the offer to 1000kg
What will happen to the demand in these cases? It will fit the offer. Some consumers will buy when the price is $ 12. Then fewer consumers will buy for $ 15. But if it charges $ 50, maybe no consumer buys! This will cause price decrease, as explained in the Law of Supply and Demand.
Therefore, demand and supply are adjustable. For different prices, there will be different demands.