hiii archit first of all find mass per unit length as density  and cross sectional area is given ...now for aluminum wire it will be 7.8*10to the power -3 and for steel u will get same...just multuply area given to density.now if mass per unit length is same for both then their wave speed will be same .now we have to find min. frequency ,for min.frequency their should be max. wavelength and for max. wavelength their should be min. loops should be produced.....now max. distance of loop can be 20 cm. i hope u will understand this from figure.,provided by me,now value of wavelenght will be 20multiply 2=40cm.now we know that wave speed= whole underoot of T/M,HERE T IS tension and m is mass per unit length now by putting the values in given formula u will get wave speed.thats it now u can calculate freq, as u know frequency=wave speed /wavelength .remember put the wavelength in m i,e 0.4m,u will get approx. 180 .hopefully this will help u,if u have any doubt u can ask me..........gud luck