$($b$)732\mathrm{.}1-(\frac{892\mathrm{.}5}{8\mathrm{.}2})=$

$($c$)[(3\mathrm{.}696*{10}^5)-(6\mathrm{.}234*{10}^3)]*0\mathrm{.}0742=$

$($d$)0\mathrm{.}006438*108-(8\mathrm{.}639+8\mathrm{.}52)=$

how to find significant figure