Help with this question pls

Answer:
Exact: [tex]4\sqrt{55}[/tex] m
Approximate: 29.7 m
Step-by-step explanation:
[tex]a^2+b^2=c^2[/tex]
[tex]9^2+b^2=(31\sqrt{5} )^2[/tex]
[tex]81+b^2=31^2(5)[/tex]
[tex]b^2=961-81[/tex]
[tex]b=\sqrt{880} =4\sqrt{55}[/tex]
[tex]4\sqrt{55}[/tex] ≈ 29.7 m
Hope this helps!