Question 417504
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Hi
Let s represent the length of a side
Question states***
  s^2 = 4s + 45
 s^2 - 4s -45 = 0
factoring
 (x+5)(x-9)=0
 (x+5)= 0  x =-5  Tossing out negative solution for length
( x-9)= 0  x = 9, the length of a side

CHECKING our Answer***
 81 = 36 + 45 = 81