In an arithmetic sequence, u, = 12 and U 10 = 40. The common difference is d. Write down two equations in u, and d to show this information. b Find the values of u, and d. a c Find the 100th term.​

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?