You traveled up the river at 56 feet a minute and down the river at 47 feet a minute.
The question is asking us to simply convert the speed traveled in feet per second to feet per minute. To do that, we say,
28 feet in 30 seconds, if we multiply both by two. We have 56 feet in 60 seconds. Also remember that 60 seconds make 1 minute. Thus, you must have kayaked up the river at 56 feet in a minute.
423 feet in 9 minutes, if we divide both by nine. We have 47 feet in a minute. This means that you kayaked 47 feet a minute down the river.
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