A reaction has an activation energy of 60kJ mol−1. At 298K, experimental data show that 4.5 % of gas molecules have kinetic energy ≥60kJ mol−1. A catalyst lowers the activation energy to 40kJ mol−1, for which 18 % of molecules have sufficient energy. By what factor does the frequency of successful collisions increase when the catalyst is present? Provide your answer as a numerical factor.