The base angle of an isosceles trianlge is ten less than thrice the vertex angle the vertex angle ?

Question

$\begin{array}{1 1} (a)\;20^{\circ} \\ (b)\;21^{\circ} \\ (c)\;22 \frac{2}{7} ^{\circ}\\(d)\;21 \frac{2}{7} ^{\circ} \end{array}$