Question

What’s the quotient of 5/31 divides by 15/21

Answer 1

Quotient just means the answer when dividing, so let's divide!:
$\frac{5}{31} / \frac{15}{21} = \frac{5}{31}* \frac{21}{15}$
$\frac{105}{465}$

Simplify (they are both divisible by 15):
$\frac{7}{31}$

And there ya go!