$\lim\limits_ { h \rightarrow 0 } \frac { f ( x + h ) - f ( x ) } { h }$

$\frac{5^{x+h}-(x+h)^3-(5^x-x^3)}{h}$

$\frac{(5^{x+h}-5^x)-(x^3+3x^2h+3xh^2+h^3)+x^3}{h}$

$\frac{5^x(5^h-1)-3x^2h-3xh^2-h^2}{h}$

Let $x=1$ and $h=0.001$.