Question 902470
This is similar triangles but can be understood to use equal slopes.  The shadow is on the ground.


One of the triangles has leg {{{h-m=8-2=6}}} and other leg {{{d=15}}}; and is a RIGHT triangle.


The other triangle has the shadow corresponding to the length d, and the man's height 2 corresponding to the 6.
{{{s/15=6/2}}}
{{{s/15=3}}}
{{{highlight(s=45)}}}