What number should be added to -1 so as to get

Let the required number be x.

Now,

$-1+x=\frac{5}{7}$

$\Rightarrow-1+x+1=\frac{5}{7}+1 \quad$ (Adding 1 to both the sides)

$\Rightarrow x=\left(\frac{5+7}{7}\right)$

$\Rightarrow x=\frac{12}{7}$

Hence, the required number is $\frac{12}{7}$.