Keristen runs a website that helps people learn programming. Every month keristen receives subscription fees of $10 from each subscriber to her website. Last month the website had 100 subscribers. This month 30 new members joined the website and 10 members cancelled their subscription. How much money will kierstens online business earn from this month?

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?