The separation of two coloured substances was done by paper chromatography. The distances travelled by solvent front, substance A and substance B from the base line are \( 3.25 \, \text{cm} \), \( 2.08 \, \text{cm} \) and \( 1.05 \, \text{cm} \), respectively. The ratio of \( R_f \) values of A to B is ________.