Answer
$25 \text{ miles}$
Work Step by Step
The rate at which the camel travels is
\begin{array}{l}\require{cancel}
\dfrac{20\text{ miles}}{8\text{ hours}}
\\\\=
2.5\text{ miles/hour}
.\end{array}
Hence, in $20$ hours, the distance the camel travels is
\begin{array}{l}\require{cancel}
\dfrac{2.5 \text{ miles}}{\text{hour}}\cdot10\text{ hour}
\\\\=
\dfrac{2.5 \text{ miles}}{\cancel{\text{hour}}}\cdot10\cancel{\text{hour}}
\\\\=
25 \text{ miles}
.\end{array}
