To find the mean, you add all the elements together, then divide by the number of elements.
Like this:
(45+48+49+40+53)/5=47
in other words the correct answer is 47 inches.
EDIT: Did the foolish mistake, of using the wrong numbers the first time. Fixed now and the answer is correct.
I think is 20 but i am not sure
Cone's volume is

where S - surface area, h - height
Surface area =

r = 18/2=9
h= 14
π = 3.14

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Simply add 5.5 feet to 1.5 feet. The answer is 7 feet below sea level.