Given the angle of displacement -time graph of the curve $v_a=30°$.

 The angle of displacement -time graph of the curve $V_b=60°$.

 We know that the slope (tangent of the angle) gives the value of the velocity.

Therefore, The velocity of the first curve is,${\mathrm{v}}_{\mathrm{a}}=\tan 30=\frac{1}{\sqrt{3}}$.

The velocity of the second curve,${\mathrm{v}}_{\mathrm{b}}=\tan 60=\sqrt{3}$

 Therefore,the ratio is.$\frac{{\mathrm{v}}_{\mathrm{a}}}{{\mathrm{v}}_{\mathrm{b}}}=\frac{{\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$\sqrt{3}$}\right.}}{\sqrt{3}}=\frac{1}{3} \mathrm{or} {\mathrm{v}}_{\mathrm{a}} :{\mathrm{V}}_{\mathrm{b}}=1:3$