#### Answer

$731$

#### Work Step by Step

The initial work shows that:
$473 = (7 \times 64) + (3 \times 8)+(1 \times 1)$
Writing 64 and 8 in base 8 gives:
$473 = (7 \times 8^2) + (3 \times 8^1) + (1 \times 1)
\\473 = 731_{\text{eight}}$
Thus,
$473_{\text{ten}}=731_{\text{eight}}$
Therefore, the missing expression in the given statement us $731$.