If the cosine of an angle in a right triangle is $$ \frac{5}...

Question Analysis
This problem tests the ability to use the cosine function to find the length of the adjacent side in a right triangle.

Key Concept Explanation
The cosine of an angle in a right triangle is the ratio of the length of the adjacent side to the length of the hypotenuse.

Step-by-step Solution
1. Identify the given values: , hypotenuse = 39 units.
2. Set up the equation: