Answer:
1.You draw the rectangle and label on one side 20m
2.Draw a diagonal line inside the rectangle an label the line as 29m
3.Extract the the newly formed right angled triangle.
4.Find the hypotenuse (a+b=c) of the right angle which will give you the value of the unknown side.
5.Calculate the perimeter which is;
P=S+S+S+S
P= 20m+9m+20m+9m
P=29m+29m
P=58m