Use the Law of Sinse: \(\displaystyle\frac{{\sin{{A}}}}{{a}}=\frac{{\sin{{B}}}}{{b}}\)

Substitute given \(A=40°,\ B=60°\), and \(a=20\), then find \(b\):

\(\displaystyle\frac{{ \sin{{40}}^{\circ}}}{{20}}=\frac{{ \sin{{60}}^{\circ}}}{{b}}\)

\(\displaystyle{b}=\frac{{{20} \sin{{60}}^{\circ}}}{{ \sin{{40}}^{\circ}}}\)

\(\displaystyle{b}={26.9}\)