Answer
$-\dfrac{5}{7}i$
Work Step by Step
Multiply both the numerator and the denominator by the conjugate of the denominator, which is $-7i$, to obtain:
$=\dfrac{5(-7i)}{7i(-7i)}
\\=\dfrac{-35i}{-49i^2}$
Use the fact that $i^2=-1$ to obtain:
$=\dfrac{-35i}{-49(-1)}
\\=\dfrac{-35i}{49}
\\=-\dfrac{5(7)}{7(7)}i
\\=-\dfrac{5}{7}i$