Answer :

that's not a squre
anyway, we use ratios
base:person to corner=28:8
height to height=x:5
so
28/8=x/5 becasue same ratio
28/8=14/4=7/2
7/2=x/5
multiply
35/10=2x/10
35=2x
divide 2
17.5=x

x=17.5 feet

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