Question
For any two points M and N in the X Y-plane, let M N denote the vector from M to N, and 0 denote the zero vector. Let P, Q and R be three distinct points in the X Y-plane. Let S be a point inside the triangle P Q R such that S P +5 S Q +6 S R = 0 . Let E and F be the mid-points of the sides P R and Q R, respectively. Then the value of length of the line segment E F length of the line segment E S is ________