#### Answer

(a)
$10$;
$e$;
change-of-base
$\log{12}$;
$\log{7}$;
$1.2770$
(b) yes

#### Work Step by Step

RECALL:
The change-of-base formula for logarithms:
$\log_a{b} = \dfrac{\log{b}}{\log{a}}$
This formula works for any base
Most calculators can compute logarithms with base $10$ and base $e$.
In using a calculator to evaluate logarithms with base other than $10$ and $e$, the change -of-base formula above will be used.
(a) Therefore, the missing expressions in the given statement (in order) are:
$10$;
$e$;
change-of-base
$\log{12}$;
$\log{7}$;
$1.2770$
(b) The change-of-base formula will give the same answer even if different bases are used. Thus, using $\ln{}$ in place of $\log{}$ will give the same answer.