Mb/s is megabit per second so when tele say 4mb it begabit not byte. To know the exaact speed u divide it by 8. Bcoz 1 byte is 8 bits. So 4mbit/8 its 0.5mbyte. So the maximum downlaod speed will be 512 kb/sec. That is if u dont lose any packets (improbable). So u shud get 450 kbyte/sec. It costs 1200 birr.