Help 100 points to answer the page

And explain how you got it so i can understand future problems : 3

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?

If 5x - 2 = -12, then x = a) -50 b) -4.4 c) -2.8 d) -2