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Area totale delle 4 fontane $\small A_{tot}= 4×3,5^2 = 4×12,25 = 49\,m^2;$
area del parco calpestabile $\small A= 40^2-49 = 1600-49 = 1551\,m^2 \Longrightarrow = 1551×10^{-2} = 15,51\,dam^2.$