Answer
$g(f(5z))=1000z^2-80z+3$
Work Step by Step
In order to find $g(f(5z))$ let's find $f(5z)$ first:
$f(5z) = 5(5z)^2-2(5z)=125z^2-10z$
Then subsitute in $g(x)$
$g(f(5z))=8(125z^2-10z)+3=1000z^2-80z+3$
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