Final answer:
The area of the square with sides of length 9z² decimeters is 81z⁴ square decimeters.
Step-by-step explanation:
The area of a square is calculated by squaring the length of one of its sides. In this case, the square has sides of length 9z² decimeters. To find the area, we square this side length:
Area = side × side = 9z² × 9z² = 81z⁴ square decimeters.
Since the units are already in decimeters, there is no need for unit conversion, and the correct number of significant figures has been maintained as per the given value of the side length.