Question

$\triangle abc$ and $\triangle def$ are similar. find the missing side length.
(the triangles are not drawn to scale.)

Explanation:

Step1: 求相似比

相似比为对应边的比值，$\frac{DE}{AB}=\frac{30}{5}=6$

Step2: 计算对应未知边长

未知边对应$\triangle ABC$的$BC$边，长度为$8\times6$
<Expression>$8\times6=48$</Expression>

Answer:

48