Astudent constructs the angle bisectors of a triangle and then uses their intersection point as the center of a circle. the student has constructed which of the following?

a. concentric circles of a triangle
b. a circumscribed circle of a triangle
c. an inscribed circle of a triangle
d. the perpendicular bisector of the triangle

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?