Resposta:
[tex]\textsf{Letra C}[/tex]
Explicação passo-a-passo:
[tex]\begin{array}{cccc}\sf M\acute{a}quinas &\sf Pec_{\!\!,}as &\sf Dias &\sf Horas \\\sf 5&\sf500&\sf5&\sf5\\\sf 10&\sf x&\sf 10&\sf 10\end{array}[/tex]
[tex]\sf x=\dfrac{500\cdot10\cdot10\cdot10}{5\cdot5\cdot5}[/tex]
[tex]\sf x=\dfrac{500000}{125}[/tex]
[tex]\boxed{\boxed{\sf x=4000}}[/tex]