Final answer:
The amount of iron needed to make the hollow iron ball is 2295.72cm^3.
Step-by-step explanation:
To calculate the amount of iron needed to make a hollow iron ball, we need to find the volume of the hollow space and subtract it from the volume of the outer ball.
The volume of a hollow sphere can be calculated using the formula:
V = (4/3)π(R^3 - r^3)
where R is the outer radius and r is the inner radius.
In this case, the outer radius is 9 cm and the thickness is 3 mm. Converting the thickness to cm, we have r = 0.3 cm.
Plugging these values into the formula, we get:
V = (4/3)π(9^3 - 0.3^3) = 2295.72 cm^3
Therefore, the answer is (d) 2295.72cm^3.