Answer
$8$
Work Step by Step
Generalized Basic Counting Principle:
Suppose there are $x$ experiments. If experiment $1$ can be performed in $n_{1}$ ways, experiment $2$ can be performed in $n_{2}$ ways, experiment $3$ can be performed in $n_{3}$ ways, and so on, then there are $n_{1} \times n_{2} \times n_{3} \times ... n_{x}$ ways of performing the $r$ experiments together.
Since some digits can be repeated, there are $2$ choices for the first digit, $2$ choices for the second digit, and $2$ choices for the third digit as well. Therefore,
$2 \times 2 \times 2 = 8$
