9708/12 Economics Oct Nov 2019 Online Test | Cambridge AS and A Level MCQ

In the diagram, ${S_1}{S_1}$ and DD represent the original supply and demand curves for an agricultural product.
Bad weather then reduces supply to ${S_2}{S_2}$.
The government does not allow the price to rise above $O{P_1}$.
How much of the product will the government have to supply from stocks if the price is to be maintained at $O{P_2}$?