How do you calculate 9.23times10^-4 - 7.85times10^-3?

$- 6.927 \times {10}^{- 3}$
$9.23 \times {10}^{- 4} - 7.85 \times {10}^{- 3} = 0.923 \times {10}^{- 3} - 7.85 \times {10}^{- 3}$
$= \left(0.923 - 7.85\right) \times {10}^{- 3} = - 6.927 \times {10}^{- 3}$