Use the definition of cosine together with the given value:

$\displaystyle{{\cos{{20}}}}^{\circ}=\frac{\text{adjacent}}{\text{hypotenuse}}\usepackage{cmbright}\Huge\$

$\displaystyle{0.94}\approx\frac{{m}}{{6}}\usepackage{cmbright}\Huge\$

$\displaystyle{6}{\left({0.94}\right)}\approx{m}\usepackage{cmbright}\Huge\$

$\displaystyle{5.64}\approx{x}\usepackage{cmbright}\Huge\$ , which rounds off to 5.6.