A man throw a stone over a cliff and hear it strikes at the bottom after 8.00sec the temperature is 25 celsius. What is the height of the cliff in km.

total time=time to fall+timefor sound

time to fall:
h=1/2 g t^2
t=sqrt(2h/g)
time for sound
t=h/velocitysound

8=sqrt(2h/g)+h/velocity sound

change variables: x=sqrt h
8=x sqrt(2/g)+x^2/vs
solve this quadratic for x, then to get h, square x