<Tr> <Td> 12.6 </Td> </Tr> <Tr> <Td> 7.8 </Td> </Tr> <Tr> <Td> <Table> <Tr> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> </Table> </Td> <Td> </Td> <Td_colspan="2"> Continental watershed, summit </Td> </Tr> <Table> <Tr> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> <Td> </Td> </Tr> </Table>

Explain the process through which the panama canal was constructed