A field service organisation repairs and maintains printing equipment for a large number of customers. It offers one level of service to all its customers and employs 30 staff. The operation's marketing vice-president has decided that in future, the company will offer 3 standards of service, platinum, gold and silver. It is estimated that platinum-service customers will require 50 per cent more time for the company's field service engineers than the current service. The current service is to be called 'the gold service'. The silver service is likely to require about 80 per cent of the time of gold service. If future demand is estimated to be 20 per cent platinum, 70 per cent gold and 10 per cent silver service, how many staff will be needed to fulfil demand?