For the following exercises, simplify the expression.
12. \(2^{2} \cdot 2^{4}\)
13. \(\frac{4^{5}}{4^{3}}\)
14. \(\left(\frac{a^{2}}{b^{3}}\right)^{4}\)
15. \(\frac{6 a^{2}-a^{0}}{2 a-4}\)
16. \(\frac{(x y)^{4}}{y^{3}} \cdot \frac{2}{x^{5}}\)
17. \(\frac{4^{-2} x^{3} y^{-3}}{2 x^{0}}\)
18. \(\left(\frac{2 x^{2}}{y}\right)^{-2}\)
19. \(\left(\frac{16 a^{3}}{b^{2}}\right)\left(4 a b^{-1}\right)^{-2}\)
20. Write the number in standard notation: \(2.1314 \times 10^{-6}\)
21. Write the number in scientific notation: 16,340,000