Line D and C shows direct variation because the line goes through the origin my good sir or ma'am :)
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➷ The formula for volume of a cylinder is:

The radius is half the diameter
Radius = 8/2 = 4
Substitute the values in:

Surface area = 
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➶ Hope This Helps You!
➶ Good Luck (:
➶ Have A Great Day ^-^
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This would be easy if you made more sense out of the question.