(1)∵ quadrilateral ABCD is a square.

∴∠BOC=90

∵OE⊥OF

∴∠EOB+∠BOF =∠COF+∠BOF =90

∴∠BOE=∠COF

OB = OC，∠OCF=∠OBE=45

∴△OEB≌△OFC

∴BE=CF=3

∴AB=CF=7

∴BF=4

According to Pythagorean theorem, EF=5.

(2)

∫△OEB?△OFC

∴ area of quadrilateral OEBF = area of delta = △ OBC =1/area of 4 square ABCD.

BC = 7

The area of the square ABCD =49

The ∴ area of quadrilateral OEBF =49/4.