The cost C of manning household is partly constant and partly varies as the number of people, the cost is 70,000 and for 10 people, the cost is 90,000 find the expression for C in terms of n ii. The weekly cost for 12 people​

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?