#### Answer

$$-\frac{21}{x^6}$$

#### Work Step by Step

To simplify this expression we multiply the factors together. First, we want to multiply the coefficients first to get:
$$-21(x^{-8})(x^2)$$
According to the product rule for exponents, if we multiply two powers that share the same base, we just add the exponents together and keep the same base. We apply this rule to the two exponents:
$$-21(x^{-8 + 2})$$
Now we add the exponents together to get:
$$-21x^{-6}$$
We want to simplify completely, so we do not want negative exponents in the solution. To get rid of the negative exponent, we use the negative exponent rule, which states that if we have a negative exponent in the numerator, we can move the exponent to the denominator and change its sign from negative to positive.
If we apply this rule, we get:
$$-\frac{21}{x^6}$$