Hello!
First you have to find the volume of the cylinder
To find the volume of a cylinder you use the equation

V is volume
r is radius
h is height
Put in the values you know and 3.14 for pi

Square the number
V = 3.14 * 9 * 7
Multiply
V = 197.82
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Next you find the volume of the sphere
To find the volume of a sphere you use the equation

V is volume
r is radius
Put in the values you know and 3.14 for pi

Cube the number

Multiply
V = 113.04
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Finally you subtract the two volumes from each other
197.82 - 113.04 = 84.78
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The answer is C)84.78
Hope this helps!