A lock on a bank vault consists of 5 dials, each of which has 25 positions. In order for the vault to open, each of the 5 dials must be in the correct position. How many possible dial codes are there for this lock

There 25 possible positions for each dial. Multiply the number of each dial by each other:

25 x 25 x 25 x 25 x 25 = 9,765,625 possible combinations.

not sure but it may be b, as i said i'm not sure.

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)