Ineed with number 1, but show work

Apositive number a or the same number a increased by 50% and then decreased by 50% of the result?

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?

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?