Here are the steps in solving the value of x in the equation.
1. Subtract 4 on both sides of the equation.
![\begin{gathered} 4+(9\text{ }ln\text{ }x)-4=15.8-4 \\ 9\text{ }ln\text{ }x=11.8 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/ncnem24jg7o58indive76yjbxz3hdjcjaz.png)
2. Divide both sides of the equation by 9.
![\frac{9\text{ }ln\text{ }x}{9}=(11.8)/(9)\Rightarrow ln\text{ }x=1.31111](https://img.qammunity.org/2023/formulas/mathematics/high-school/zrf090vrwfgihyr9zliwvw4g8inc9v6rt0.png)
3. By definition of natural logarithm:
![ln\text{ }x=y\Leftrightarrow e^y=x](https://img.qammunity.org/2023/formulas/mathematics/high-school/ar8fyohrlkr7cj17v35jr1pgzkdwggzd2d.png)
We can rewrite ln x = 1.3111 as:
![e^(1.31111)=3.71](https://img.qammunity.org/2023/formulas/mathematics/high-school/jwa16pumb58lyzpta25lh82asegfy6bd5u.png)
Therefore, the value of x is 3.71. (Option D).