You are able to walk uphill at a speed of 2 miles per hour and downhill at a speed of 3 miles per hour. what does the graph represent?

The slope from 0 to 3 hours is 2 miles per hour.  The slope from 3 to 4 is 3 miles per hours.

So we conclude you went uphill for three hours and downhill for 1.  You have another hour to go before your back where you started.

The slope is 6/3 = 2 for time ≤ 3, so we presume this represents an uphill walk of 3 hours. The slope increases after that, suggesting a downhill walk. The lower-left selection is indicated.