Find A^c U B if sample space S = {1 to 20}, A = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, and B = {2, 4, 6, 8, 7, 10, 12, 14, 16, 18}

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?