Question 1114544
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Let the dimensions be 3x, 5x, and 9x.  Then the volume is<br>
{{{(3x)(5x)(9x)=8640}}}
{{{135x^3 = 8640}}}
{{{x^3 = 64}}}
{{{x = 4}}}<br>
The dimensions are 12, 20, and 36.<br>
The surface area in cm^2 is
{{{2(12*20+12*36+20*36) = 2(1392) = 2784}}}<br>
A square cm is 100 square mm, so...<br>
Answer: surface area is 278400 mm^2.