What should be subtracted from $-\dfrac{7}{8}$ so as to get $\dfrac{5}{12}$?

1. $\dfrac{31}{24}$

2. $\dfrac{8}{5}$

3. $\dfrac{-31}{24}$

4. $\dfrac{-6}{8}$

Let the required number be $x$.

According to the given condition,

$\Rightarrow \dfrac{-7}{8} - x = \dfrac{5}{12} \\[1em] \Rightarrow x = \dfrac{-7}{8} - \dfrac{5}{12} \\[1em] [\text{ LCM of } 8 \text{ and } 12 = 24] \\[1em] \Rightarrow x = \dfrac{(-7) \times 3 - 5 \times 2}{24} \\[1em] \Rightarrow x = \dfrac{-21 - 10}{24} = \dfrac{-31}{24}$

Hence, Option 3 is the correct option.