Question 256309
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From the problem, it is indeed a magnification of similar triangles
{{{drawing (300,300,-1,10,-1,7,triangle(0,0,0,5,6,0),triangle(6,0,6,2,10,0),green(line(0,-.1,0,-.3)),green(line(6,-.1,6,-.3)),green(line(10,-.1,10,-.3)), green(arrow(0,-.2,6,-.2)), green(locate(3,-.4,11m)),green(arrow(6,-.2,10,-.2)), locate(6.5,-.4,shadow=x), green(arrow(5.8,0,5.8,2)),green(locate(6,1.7,1.5m)), green(arrow(-.2,0,-.2,5)), green(locate(0.1,4,6m)))}}}

The sides of the  angels are in the same ratio:
{{{6/1.5=11/x}}}
{{{6x=(1.5)(11)=16.5}}} ---> {{{cross(6)x/cross(6)=cross(16.5)2.75/cross(6)}}}
{{{red(x=2.75m)}}}, Length of shadow, Answer


Thank you,
Jojo</font>