The description of the garden fits that of 3 squares arranged side-by-side. The area of each of those would be 100 ft², so their side length would be ...
s = √A= √(100 ft²) = 10 ft
This dimension is the width of the garden, whose length is 3 times this amount.
The length and width of the garden are 30 ft and 10 ft, respectively.
You have to find the difference in height between both checkpoints. To do this just calculate 196 - 52. Checkpoint 5 is 144 (meters?) higher than Checkpoint 2.