hello,

to #9:

use the base 8 at both sides of the equation:

. Please continue.

to #10:

. Please continue.

to #11:

. Please continue.

to #12:

to #13:

use the property:

to #14:

use the property:

to #15:

you are supposed to know:

It doesn't matter which logarithmetic function you use. You should come out with