First, cotangent equals the reciprocal of tangent. Next, you need to use the definitions of cosine and tangent together with the given values to find the sides of a right triangle that would have those ratios. A triangle with $\displaystyle{a}{d}{j}={20}\usepackage{cmbright}\Huge\$ , $\displaystyle{h}{y}{p}={29}\usepackage{cmbright}\Huge\$ , and $\displaystyle{o}{p}{p}={21}\usepackage{cmbright}\Huge\$ will have these ratios. Use this information and the definition to find the value of sine.