Two identical guitar strings are stretched with the same tension...

Question

Introduction: Find the length of low-pitched string considering beat frequency
                        
More Details: Two identical guitar strings are stretched with the same tension between supports that are not the same distance apart. The fundamental frequency of the higher-pitched
            string is 340Hz, and the speed of transverse waves in both wires is 150 m/s. How much longer is the lower-pitched string if the beat frequency is 5Hz?
            
            I tried using the equation L=v/(2*fundamental freq) then doing L=v/(2*(highfreq-lowfreq)) then solving (answer 2- answer 1) but my answer is wrong.