A cellphone tower casts a shadow 30 feet long at the same time that a man 6 feet tall
cast a shadow of 2.4 feet. How tall is the
cellphone tower?

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?