The formula to calculate the lateral area of a cone is given by

where
LA=10.5pi in2
r=2.1 in
l=? slant height
substitute given values

<h2>The answer is 5 inches</h2>
The answer is 1/3 of 12 its just easy math for me
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If this is a 30, 60, 90 triangle, which I think it is, it would b 4