Current Electricity

In an experiment to find emf of a cell using potentiometer, the length of null point for a cell of emf \(1.5 \mathrm{~V}\) is found to be \(60 \mathrm{~cm}\). If this cell is replaced by another cell of emf E, the length-of null point increases by \(40 \mathrm{~cm}\). The value of \(E\) is \(\frac{x}{10} V\). The value of \(x\) is ____________.