Use benchmarks to estimate the value of each logarithm to the nearest tenth.
log_2(6.5)
I'm not sure what it means to "use benchmarks"; but:
21 = 2
22 = 4 ---> log24 = 2
23 = 8 ---> log28 = 3
So: log26.5 is somewhere between 2 and 3; I would guess that it's about 2.5.