First of all, draw a diagram.
Since OE is perpendicular to chord AB, E bisects AB. Similarly, F bisects CD.
Since AB = CD and E and F are respective bisectors, EB = FC
Draw radii OB and OC.
Since any two radii of a given circle have the same length, OB = OC.
ΔOEB and ΔOFC are congruent by Hypotenuse Leg Theorem.
Since corresponding parts of congruent triangles are congruent, OE = OF
So, 4x - 5 = 3x + 6. Therefore, x = 11. So, OE = 39