Doubt in 2009 paper Q1A

In the 2009 paper, Q1A is to prepare the return objective and state the calculation for pre-tax nominal income. the income tax rate is not mentioned all through the case (I read it 3 times just to make sure!!) however,the solution assumes (I believe) 20% tax rate. I remember reading that if the question requires you to assume any amount re-read the question. I have no hint where the 20% came from?
Any help!! @Zee @Sophie @Marc