$3^{(5-10)}$

$3^{-5}=\frac{1}{3^5}$

Remember, when an exponent is located outside of a set of parentheses, the exponent applies to every term inside the parentheses.

$10x^4(10^{-2}x^{-2})$

$\frac{{\it x}^{2}}{10}$

This can be rewritten as:

$(4^{-1})^3(4)^2$

See part (b).

See part (a) and (b).