$\begin{array}{l}\text{Here,}\\ \\ \Rightarrow \sqrt{\text{(2704}}\text{ + 78)}÷\text{13+ ?\% of 70 = 31}\\ \\ \Rightarrow \text{(52+ 78)}÷\text{13+}\frac{70x}{100}\text{= 31}\\ \\ \Rightarrow \text{130}÷\text{13+}\frac{70x}{100}\text{= 31}\\ \\ \Rightarrow \text{10+}\frac{7}{10}x\text{= 31}\\ \\ \Rightarrow \frac{7}{10}x\text{\hspace{0.17em}= 31}-\text{10}\\ \\ \Rightarrow x=\frac{\text{21}\times \text{10}}{7}\\ \\ \text{= 30.}\end{array}$

Hence, Option D is correct.