Juan accepted a job to roof a new house. He calculated that he can complete the job in
20 hours. He hired a trainee to assist him. He has seen the trainee work and estimates
that the trainee working alone would take 25 hours to complete the job. How much time
should the two of them working together need to roof the house? (Round your answer to
the nearest tenth.)

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?