Chapter 7 - Exponents and Exponential Functions - 7-3 Multipying Powers with the Same Base - Practice and Problem-Solving Exercises - Page 430: 51

$2.7 \times 10^{-8}$

$a^m \cdot a^n = a^{m+n}$ Multiply the corresponding parts and use the rule above when necessary to obtain: $=(9\cdot 3) \times (10^{7} \cdot 10^{-16}) \\=27 \times 10^{7+(-16)} \\=27 \times 10^{-9} \\=(2.7)(10) \times 10^{-9} \\=2.7 \times 10^{1+(-9)} \\=2.7 \times 10^{-8}$