You are standing on the middle rung of a ladder. if you first climb up 3 rung then down 5 rung and then up 10 rung to get onto the top rung how many rung are on the ladder

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?