First use your calculator to find $\displaystyle{{\tan{{20}}}}^{\circ}\approx{0.3639702343}\usepackage{cmbright}\Huge\$ .

Then find the reciprocal of this: $\displaystyle{{\cot{{20}}}}^{\circ}=\frac{{1}}{{{{\tan{{20}}}}^{\circ}}}\approx{2.747477419}\usepackage{cmbright}\Huge\$

Finally, round off to 2.747.