<Tr> <Td> Vietnam </Td> <Td> 40 </Td> <Td> Monday--Friday </Td> <Td> 8 </Td> </Tr> <Tr> <Td> Yemen </Td> <Td> 40 </Td> <Td> Sunday--Thursday </Td> <Td> 8 </Td> </Tr> <Tr> <Td> Congo, Democratic Republic of </Td> <Td> 40 </Td> <Td> Monday--Friday </Td> <Td> 8 </Td> </Tr> <Tr> <Td> Zambia </Td> <Td> 40 </Td> <Td> Monday--Friday </Td> <Td> 8 </Td> </Tr>

What invention extended the working hours in a day