1. Multiply and simplify the expression: $(x^2 - 4x - 21) \cdot \frac{10}{5x + 15}$. The simplified product is ___.
2. What is the simplified product of $\frac{x^2 - 4}{x^2 + 7x + 10} \cdot \frac{x+5}{x-2}$?
3. Multiply and simplify the expression: $\frac{5x^4}{6y^2} \cdot \frac{18y}{10x^2}$. The simplified expression is ___.
4. Multiply and simplify the following expression: $\frac{6}{x^2 + x - 12} \cdot (x-3)$.
5. What is the simplified product of $\frac{x^2+2x-15}{1} \cdot \frac{7}{2x-6}$?
6. Multiply and simplify the expression completely: $$\frac{5a^4}{2b} \cdot \frac{8b^3}{10a^2} = \_\_\_$$
7. Simplify the expression: $$\frac{x+5}{x-1} \cdot \frac{x^2-1}{x^2-25}$$
8. Multiply the rational expressions and simplify the result: $$\frac{x^2-4x+4}{x+3} \cdot \frac{x+3}{x-2} = \_\_\_$$
9. When simplifying the expression $\frac{x^2-9}{x+3}$, what is the correct and most crucial first step?
10. Find the product and simplify: $$\frac{7m^5}{3n^2} \cdot \frac{6n}{14m^2} = \_\_\_$$