Question 596766
Hello, 
This could be written 2 different ways, so I'll solve both ways.
1) n^2+(3n)^2=81
   10n^2=81
    n^2=8.1
   Sqrt both sides and we get:
    n=2.846 (approx)

2)n^2+3n^2=81
  4n^2=81
   n^2=20.25
  Sqrt
   n=4.5
Make sense?
RJ
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