I start school December 2

Three times the sum of a number and seven is negative thirty-six. what is the number?

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?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.