1. **State the problem:** Simplify the expression consisting of three parts: $6a^3$, $\frac{5b}{21a}$, and $10b^2$. 2. **Analyze each part:** - The first part is $6a^3$, which is already simplified. - The second part is a fraction $\frac{5b}{21a}$. - The third part is $10b^2$, which is also already simplified. 3. **Simplify the fraction $\frac{5b}{21a}$:** - Find the greatest common divisor (GCD) of numerator and denominator coefficients: GCD of 5 and 21 is 1. - Since GCD is 1, the fraction cannot be simplified further. 4. **Final simplified expression:** - The expression remains as three separate terms: $$6a^3, \quad \frac{5b}{21a}, \quad 10b^2$$ No further simplification is possible without additional operations such as addition or multiplication between these terms.