Hello, symmetry!
To measure the distance $\displaystyle DC$ across a pond,
a surveyor takes points $\displaystyle A$ and $\displaystyle B$ so that $\displaystyle AB \parallel DC$.
If $\displaystyle AB = 60\text{ ft},\;EB = 48\text{ ft},\;ED = 80\text{ ft}$, find $\displaystyle DC$. You forgot to tell us where point $\displaystyle E$ is, but I have a good guess. Code:
D * - - - - - - - - - - - - - - - * C
* *
80 * *
* *
*E
* * 48
* *
A * - - - - - - - - - - - * B
60
From the similar triangles, we have: .$\displaystyle \frac{CD}{80} \:=\:\frac{60}{48}$
Therefore: .$\displaystyle CD \:=\:100\text{ ft}$