What is the same as moving the decimal point 3 places to the right in a decimal number?

What is the y-intercept of the line given by the equation

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?

3x + 4y = 5 x- 3y = -7 solve by substitution