Answer
$40a^{19}$
Work Step by Step
$5a^{7}(2a^{4})^{3}=5a^{7}\times2^{3}\times(a^{4})^{3}=5a^{7}\times8\times a^{4\times3}=5a^{7}\times8\times a^{12}=5\times8\times a^{7}\times a^{12}=40\times a^{7+12}=40\times a^{19}=40a^{19}$
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