It appears that you found the value of $\displaystyle{\csc{{A}}}\usepackage{cmbright}\Huge\$ . Remember that the two acute angles in a right triangle will have different trigonometric ratios. First use the Pythagorean Theorem to find b:

$\displaystyle{{b}}^{{2}}+{{6}}^{{2}}={{7}}^{{2}}\usepackage{cmbright}\Huge\$

After solving this equation, substitute the value of b for the opposite side in the definition of cosecant.