خطا
$\begin{align} & D+{{C}_{2}}+{{C}_{3}}+{{B}_{2}}={{180}^{\circ }}\quad * \\ & 2{{C}_{2}}=110+{{B}_{1}}+{{B}_{2}}\to 2{{C}^{2}}=110+2{{B}_{2}}\to {{C}_{2}}=55+{{B}_{2}}\quad ** \\ & {{C}_{3}}+A+{{B}_{1}}+{{B}_{2}}=180\to {{C}_{3}}+A+2{{B}_{2}}=180\to {{C}_{3}}=180-110-2{{B}_{2}}=70-2{{B}_{2}}\quad *** \\ & *,**\to ***\quad D+{{C}_{2}}+{{C}_{3}}+{{B}_{2}}={{180}^{\circ }}\to D=180-{{B}_{2}}-55-{{B}_{2}}-70+2{{B}_{2}}=180-55-70={{55}^{\circ }} \\ \end{align}$