Take out 6.345 from 8.1.

Converting the given decimals into like decimals, we have to subtract 6.345 from 8.100.

Subtracting columnwise, we get:

$\begin{array}{r} 8.100 \ -\phantom{0}6.345 \ \hline 1.755 \ \hline \end{array}$

Hence, the answer is 1.755