1. a source of sound is directed a large brick wall. a girl walks towards the wall and notices that the intensity of the sound decreases to aminimum every 50cm. what is the frequency of the sound? the air temperature is 20 degrees celsius (answer is 344Hz) 2. attempted to use the universal wave equation, being V = frequency x lambda 3. found new velocity of sound to be 343.2m/s by doing 331.4 m/s (0.59)(20degrees celsius) took this new velocity, and attempted to put it into the above listed equation in #2, although the equation is meant for the velocity of a WAVE, i did not know which equation to use. help please and thanks !?