What is the equation for this line?

a. 3x - 5y = 15
b. -5x + 3y = -15
c. 5x - 3y = -15
d. 3x - -5y = -15

i selected c, but i want to make sure i'm correct though as i'm not very certain.

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?