After 63 litres of petrol was poured into an empty storage tank, it was still 10% empty. How much more petrol (in litres) must be poured into the storage tank in order to fill it completely?

In a town with 30,000 professionals, teachers make up 11% of the total professionals. If 46% of teachers are male, what is the number of female teachers in the town?

In a town's professional breakdown, doctors represent 18% and clerks represent 8% of the total professionals. If the number of doctors is 3000 greater than the number of clerks, what is the total number of professionals in the town?