4. Do the problem!

In the following image, \(HOLD\) is a rectangle with \(E\) and \(R\) are mid-points of \(HD\) and \(HO\) respectively. If \(OL\) \(=\) 12 \(cm\) and \(LD\) \(=\) 35 \(cm\), then find the length of \(ER\).

 

 

The length of \(ER\) is: