Adult height is somewhat predictable from average height of both parents. For females, a commonly used equation

Question:

Adult height is somewhat predictable from average height of both parents. For females, a commonly used equation is YourHeight = ParentHeight – 2.5 while for males the equation is YourHeight = ParentHeight + 2.5.
(a) Test these equations on yourself (or on somebody else).
(b) How well did the equations predict your height?
(c) How do you suppose these equations were derived?