9 is your answer
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Using Pythagorean theorem
[tex]\\ \sf\longmapsto B^2=H^2-P^2[/tex]
[tex]\\ \sf\longmapsto B^2=(√97)^2-4^2[/tex]
[tex]\\ \sf\longmapsto B^2=97-16[/tex]
[tex]\\ \sf\longmapsto B^2=81[/tex]
[tex]\\ \sf\longmapsto B=9[/tex]
