From the right angled triangle given,
To find the missing side, x, of the triangle, Pythagorean theorem is applied
The Pythagorean theorem formula is

The dimensions of the triangle are
![\begin{gathered} \text{Hyp}=\sqrt[]{10}mi \\ \text{Opp}=xmi \\ \text{Adj}=3mi \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/sjqiwdivguobgln4z0ng9lonbql6jt885l.png)
Substituting the values into the Pythagorean theorem formula above,
![\begin{gathered} (\sqrt[]{10})^2=x^2+3^2 \\ 10=x^2+9^{} \\ \text{Collect like terms} \\ x^2=10-9 \\ x^2=1 \\ \text{Square root of both sides} \\ \sqrt[]{x^2}=\sqrt[]{1} \\ x=1 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/jcf6ig05atuwq0759ylj2iyip98rhgb7n2.png)
The missing side, x is 1mi
Answer is D