In the above figure, O is the center of circle. Angle AOB=90∘. The line AC is parallel to OD. OB's length is equal to twenty centimeters. BD's length is equal to four centimeters. Determine the length of AB.

Line BC may or may not be parallel to line AO.

If AC is parallel to OB, that doesn't make BC parallel to AO.

There's not enough informatio for this problem to be solved!!!