The Pythagorean Theorem gives you:

$\displaystyle{{b}}^{{2}}+{{6}}^{{2}}={{7}}^{{2}}\Rightarrow{{b}}^{{2}}+{36}={49}\Rightarrow{{b}}^{{2}}={13}\Rightarrow{b}=\sqrt{{13}}\usepackage{cmbright}\Huge\$

Then:

$\displaystyle{\csc{{B}}}=\frac{{h}}{{o}}=\frac{{7}}{\sqrt{{13}}}\usepackage{cmbright}\Huge\$