(4a) What is the problem being addressed by a sugary drinks tax? State the problem in terms of the concept of 'externalities', ensuring you explain the link between this concept and sugary drinks. Explain how the tax is able to address the problem. [3 marks] (4b) [graph] Depict on a graph a perfectly competitive market with the externality you discussed in (4a). Utilise the graph to clearly highlight and discuss the problems associated with this externality. [hint: focus on the quantity difference between the market equilibrium and the socially desirable equilibrium] Now consider what happens if the market consolidates and becomes a monopoly (there is no need to depict this on the graph). Do you think the externality problem you previously highlighted will increase or decrease? [hint: focus on the quantity difference between a monopoly and perfectly competitive market]