The water level of a river in the town of Carson decreased by 41/4 feet over a 3­month period. Which of these describes the average monthly change in the water level of the river? SHOW YOUR WORK IN A PIC OR I WONT MARK BRAINLIEST

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?