Solve the following pair of linear equations
3/x - 1/y = -9
And
2/x + 3/y = 5

Which expression is equivalent to (9x - 3 1/ + 1 3/8)

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?

What is the circumference of a circle with an area of 50.24 cm²?