If the plot is 60 square meters in area and 10 meters long then we can divide the area (60 square meters )by the length (10 meters) to get the missing side of 6 meters. Since the plot is rectangular there are 2 sides that are 10 meters and 2 sides that are 6 meters. Add up all the sides 2(10+6) [or just 10+10+6+6] to get a final length of 6 meters of white picket fence.