121 meters
1) Since those triangles share a parallel side, then we can use the Thales Theorem to find out the missing side. So we can write:
[tex]\begin{gathered} \frac{100}{220}=\frac{55}{x} \\ 100\cdot x\text{ =55}\cdot220 \\ x=\frac{55\cdot220}{100} \\ x=121 \end{gathered}[/tex]
2) Hence, we can state that the distance across Copperfield lake is 121 meters
