A contractor has $3,285 to spend for doors and hammers. Doors cost $75 each. He bought the greatest number of doors that he could buy. He will use the money he has remaining to buy hammers that cost $15 each. What is the greatest number of hammers the contractor can buy with the money he has remaining?

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?