HELP QUICK it is for Geometry

Ascatterplot is produced to compare the size of a school building to the number of students at that school who play an instrument. there are 12 data points, each representing a different school. the points are widely dispersed on the scatterplot without a pattern of grouping. which statement could be true

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?

X+y=-4 x-y=2 use elimination with adding and subtraction