Financial intervention to overcome market failure

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Today I was talk about financial intervention to overcome market failure, this title like the last one, but it's different.
Market failure is when the free market mechanism fail to achieve economy efficiency.
Financial intervention is a intervention of government to correct the market failure by

If the government want to make something more expensive, they can use taxation.
If the government want to make something cheaper, they can use subsidies.
Let's talk about tax, they uses taxation on market failure when is negative externality and demerit goods which is over consume .(draw a diagram 1)


This diagram shows because of too much of products consumed, and a lot of produce of a firm. So what should the government do? They increase the indirect tax on the product. So because of the high tax to produce to a firm , therefore the supply curve shift to the left,as the supply curve shift to the left, that means the price increase from P to P1, therefore with out increase in price, the quantity will shift to the left from Q to Q1. So here, financial intervention to overcome market failure because less consume, less quantity and less produce. So there will more allocation efficiency to use scarce resources.
For positive externally and merit goods,they are under consume and under produce, so the government need subsidize them to increase the produce. So after subsidize the cost of produce is reduced,Supply curve shift to the right, and then the price goes down,also the quantity shift ti the right from Q to q1in this case , the resources allocate more efficiency , therefore the market failure is overcome(draw a diagram 2)