I2.2 In the figure, $P A$ touches the circle $A B C$ at $A, P B C$ is a straight line, $A B=P B, \angle A C B=a^{\circ}$. If $\angle A B P=b^{\circ}$, find the value of $b$.
$\begin{array}{l}\angle B A P=a^{\circ}=38^{\circ}(\angle \text { in alt. seg. }) \\ \left.\angle B P A=38^{\circ} \text { (base } \angle \text { s isos. } \triangle\right) \\ 38+38+b=180(\angle \text { s sum of } \triangle) \\ b=104\end{array}$