Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph... sorry couldn't find anymore info from my teacher, well I couldn't remember all of it.
Out of the four options presented in this problem, the most probable answer would be A. humidity.
Weather has many characteristics which includes, but are not limited, to air temperature, wind speed, the directions of the wind, cloud cover, the type of clouds present, amount of precipitation, the type of precipitation, and of course humidity. Although B. winds is an option, it isn't ultimately a main characteristic since some weathers doesn't involve winds too much. The humidity, however, is present in all kinds of weather. The other characteristics help in differentiating which weather to which weather.
270/70^2 = x/80^2
Cross multiply
270 (6400) = 4900x
x = 270(6400)/4900
352 and 32/49 feet
Hope this helps