<p>已知图4-20所示结构中的q、L,则固定端B处约束力的值为(设力偶逆时针转向为正)() <img alt="" src="https://file.gaojiufeng.cn/learnAppQuestion/98/bd/98bd6b6a7d24f49267a12ed768085253.jpg" style="width: 100%;height: auto;"><img alt="" src="https://file.gaojiufeng.cn/learnAppQuestion/b6/9f/b69fca9a4e49d416cb279b1733f3fbba.jpg" style="width: 100%;height: auto;"></p>