A regular star is equilateral and has congruent angles at the vertices and congruent angles at each indentation. Given the following examples of regular stars, give a rule for the number of lines of symmetry in a regular star. In two or more complete sentences, justify the rule.

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?