Answer: A. $5$

Explanation:

1. Start with the given equation:

   $9n - 10 = 2n + 25$

2. Isolate the variable term (n) on one side of the equation:

   - To do this, we can subtract $2n$ from both sides:

     $9n - 2n - 10 = 2n - 2n + 25$

     $7n - 10 = 25$

3. Isolate the constant terms on the other side:

   - Add 10 to both sides of the equation:

     $7n - 10 + 10 = 25 + 10$

     $7n = 35$

4. Solve for n:

   - Divide both sides by 7:

     $\dfrac{7n}{7} = \dfrac{35}{7}$

     $n = 5$

5. Conclusion:

   - The solution to the equation is $n = 5$ , which corresponds to option A.