Answer
$-140x^{12}$
Work Step by Step
We are given the expression $-7x^{3}\times20x^{9}$. We can simplify by grouping like terms.
$(-7\times20)\times(x^{3}\times x^{9})$
Next, we can use the product rule, which holds that $a^{m}\times{a^{n}}=a^{m+n}$ (where a is a real number, and m and n are positive integers).
$-140\times(x^{3+9})=-140x^{12}$