In the figure, an aluminum wire, of length L1 = 356 cm, cross-sectional area 7.00×10-2 cm², and density 2.60 g/cm³, is joined to a steel wire of density 7.80 g/cm³ and the same cross-sectional area. The compound wire, loaded with a block of mass m = 4.00 kg, is arranged so that the distance from the joint to the supporting pulley is L2 = 82.2 cm. Transverse waves are set up on the wire by an external source of variable frequency; a node is located at the pulley. Find the lowest frequency that generates a standing wave having the joint as one of the nodes. How many nodes are observed at this frequency?