What should be added to $\dfrac{-3}{16}$ to get $\dfrac{5}{8}$ ?

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

2. $-\dfrac{1}{2}$

3. $\dfrac{3}{8}$

4. $\dfrac{13}{16}$

Let the number be x.

$x + \Big(\dfrac{-3}{16}\Big) = \dfrac{5}{8} \\[1em] x = \dfrac{5}{8} + \dfrac{3}{16} \\[1em]$

L.C.M of 8 and 16 is 16.

Now, expressing each fraction with denominator 16:
$x = \dfrac{5 \times 2}{8 \times 2} + \dfrac{3 \times 1}{16 \times 1} \\[1em] x = \dfrac{10}{16} + \dfrac{3}{16} \\[1em] x = \dfrac{13}{16}$

Hence, option 4 is the correct option.