X-3x+4=3-9 what is x?

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?

Raymond just got done jumping at super bounce trampoline center. the total cost of his session was $43.25 . he had to pay a $7 entrance fee and $1.25 for every minute he was on the trampoline. write an equation to determine the number of minutes (t) that raymond was on the trampoline.

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?