find the missing side of triangle

Using Pythagoras Theorem
[tex]\\ \sf\longmapsto B^2=H^2-P^2[/tex]
[tex]\\ \sf\longmapsto B=\sqrt{H^2-P^2}[/tex]
[tex]\\ \sf\longmapsto B=\sqrt{29^2-21^2}[/tex]
[tex]\\ \sf\longmapsto B=\sqrt{841-441}[/tex]
[tex]\\ \sf\longmapsto B=\sqrt{400}[/tex]
[tex]\\ \sf\longmapsto B=20[/tex]