Timetakentogo30kmdownstream=3015+xhrTimetakentocomeback=3015−xhrFromthegiveninformation3015+x+3015−x=430603015+x+3015−x=92450−30x+450+30x(15+x)(15−x)=92900225−x2=92100225−x2=12225−x2=200x2=25x=±5Butxcannotbenegative,sox=5Thusthespeedofthestreamis5km/hr