The Area of a geometric figure can be calculated based on the appropriate formulas.
For example, the area of a rectangle is based on the size of their sides: width and length
In your example, it seems that the length of the rectangle is 8.5 m and its width (shorter side) is 8 m.
Therefore, the area i calculated via the formula:
Area Rectangle = base x height
Area = 8.5 m x 8 m = 68 square meters
(we are here assuming that the base is the longest side)