Answer:
36 miles
Explanation:
Let's go ahead sketch the given problem as shown below;
From the above diagram, we can go ahead and determine x, which is the distance the eastbound plane has traveled, using the Pythagorean theorem;
[tex]\begin{gathered} 39^2=x^2+15^2 \\ 1521=x^2+225 \\ x^2=1521-225 \\ x=\sqrt[]{1296} \\ x=36\text{miles} \end{gathered}[/tex]