\text { 10. } \frac{21 x}{4} \cdot \frac{2 y}{3}= \frac{-30 r s}{-6} \cdot \frac{p}{5}= \frac{4 y}{-6} \cdot \frac{s}{4}= \frac{10 m}{-3} \cdot \frac{n}{2}=