What's 12p+5pd-3p+6pd

What is the value of x in the this question ?

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?

Find the solution(s) to the system of equations. select all that apply y=x^2-1 y=2x-2