Help with economic question

The UK's macroeconomic objectives is a stable low inflation (2%), a sustainable expansion (real) rate (2.5%), a balance of payments on the current account and a full employment (full - unquantified, normally 3-5%)

You could start by defining supply-side policies and macroeconomic objectives.

You could then start by listing the benefits of supply-side policies while broadly keeping to the question by mentioning the examples, such as
1) LRAS rightward shift (expand - increases aggregate output which will increase unemployment and decreases price level which lowers inflation)
Draw a graph here

2) (Linking to the question) Improves labour market rigidities by having more competition resulting in more productivity, this reaches the growth
objective /// Here you can talk about labour mobility instead of changes to labour law

3) (Linking to the question) Building infrastructure can improve the trade balance by making it cheaper and more efficient for domestic producers to expand and export through your reasons and those stated above)

Disadvantages of supply-side policies
1) Government failure in implementing policies can lead to adverse effects
2) Exogenous effects could ruin attempts at supply side policies, such as an economic crisis at the UK's main export destinations
3) Here I would talk about the time lag of supply side policies, their biggest disadvantage, however, exam boards since 2014 have made it clear that students ought to consider effects on income and wealth of macroeconomic policies, so unless you mention them in one of those above, talk about them here, in which case, supply-side policies often have an adverse effect on income and wealth, at least in the short-term, especially labour market reform.

Alternatives to supply-side policies
1) Monetary
2) Fiscal
3) Lack of state intervention

Conclusion
Which is best, which is best/worst in short term, which is best/worst in long term, and then link back to the question by saying which is most likely to push the UK to reach the macroeconomic objectives and finish by talking about a scenario when supply-side policies could be used IF you concluded they aren't the most likely to make the UK reach its goals.

Thank you! Also, i wanted to ask, if you aggregate output increase how does increase in unemployment occur?

My apologies I meant an increase in a aggregate output will increase employment.