Question 199853
A rough  sketch  shows  similar  triangles,  therefore  proportions  are  appropriate,,(use  tan  function  if  more  comfortable)
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3/4 = h / 72,,,cross  multiply
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4h = 216
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h=54
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check  ,,,fence  shadow is  1/3  more ( 1/3),,,  and  pole  shadow  is  also  1/3 more ( 18/54=1/3),  ok

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