Find the sum of the first 30 terms of the sequence 3, 7, 11, 15

Need this asap if anyone can i would be very grateful. if you could show workings that would really

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?

How are algebraic expressions evaluated using substitution?