Answer:
x=2.4650
Step-by-step explanation:
I assume that you mean 
so let s use the ln() function

so x = ln(15)/ln(3)
x = 2.4650
Answer: 7
How many took 7.5 OR less. This means it includes the hikes that took 7.5 hours. Count all of the ones that start from 7.5 and lower