since ln(x) is a strictly increasing function

1. ln2 < ln3 < ln6

also because ln(a) + ln(b) = ln(ab)

ln2 + ln3 = ln6

2. same here:

ln4 < ln5 < ln20

ln4 + ln5 = ln20

3.one of the properties of the ln function is: ln(a^b) = b*ln(a)

ln(3^5) = 5*ln3

you might also consider reading:

Natural logarithm - Wikipedia, the free encyclopedia