We know the Margin of Safety = Amount of profit / (p/v ratio)

Now in our given problem , Amount of profit is Rs.18000 and p/v ratio is 50%.Thus by substituting the values in the above formulae of Margin of Safety we get,

Margin of safety = 18000/50% =Rs.36000

Thus the Margin of safety for the given case is Rs.36000.

I hope my answer helps you. All the very best for your future endeavors!