Question 999930
Okay, from
1/10 = (1/2)^(30/h) 
you just take the ln first...
ln(1/10) = ln[(1/2)^(30/h)]
ln(1/10) = (30/h)ln(1/2) 
since ln(1/x) = -ln x, we get
-ln10 = (30/h)(-ln2)
and
30/h = -ln10/-ln2 = ln10/ln2
and rearranging gives
h = 30/(ln10/ln2) = 30 ln 2 / ln 10 = 9.03