What are the names of four coplanar points

Which statement justifies why angle ebc measures 90?

What are the coordinates of the point that is 1/3 of the way from a to b? a (2,-3) b (2,6)

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?