A system uses the Go-back-N ARQ protocol with a window size of 7. If each packet carries 1000 bits of data, how long does it take to send 1 million bits of data if the distance between the sender and receiver is 5000 Km and the propagation speed of the signal is 2x10^8 meters per second? Ignore transmission, waiting, and processing delays. Assume no errors in the link.