In the following figure, \(ABCD\) is a rhombus. Diagonals \(AC\) and \(BD\) intersect at \(O\). \(E\) and \(F\) are mid-points of \(OA\) and \(OB\) respectively. If \(AC\) \(=\) 42 \(cm\) and \(BD\) \(=\) 56 \(cm\), then \(EF\) is:
The value of \(EF\) \(=\) \(cm\)