Find the value of $(5a^6) \times (-10 ab^2)\times (-2.1a^2b^3)$ for $a=1$ and $b=\large\frac{1}{2}$

Question

$\begin{array}{1 1} 105 \\ \large\frac{105}{30} \\ \large\frac{105}{32} \\ \large\frac{105}{42} \end{array} $