\(476-\left\{5.\left[409-\left(8.3-21^2\right)\right]-1724\right\}\)
\(=476-\left\{5.\left[409-\left(24-21\right)^2\right]-1724\right\}\)
\(=476-\left\{5.\left[409-3^2\right]-1724\right\}\)
\(=476-\left\{5.\left[409-9\right]-1724\right\}\)
\(=476-\left\{5.400-1724\right\}\)
\(=476-\left\{2000-1724\right\}\)
\(=476-276=200\)