A block (mass = 15.1 kg) is held in position on a frictionless incline by a cord (length = 0.604 m). The mass per unit length of the cord is 1.21e-2 kg/m, so the mass of the cord is negligible compared to the mass of the block. The cord is being vibrated at a frequency of 169 Hz (vibration source not shown in the drawing). What is the smallest angle θ between 15.0degree and 90.0degree at which a standing wave exists on the cord?