Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 69

$1.45\times10^{8}$

Using laws of exponents, the given expression simplifies to \begin{align*} & (5\times10^{11})(2.9\times10^{-3}) \\\\&= (5\times2.9)(10^{11}\times10^{-3}) \\\\&= 14.5\times10^{11+(-3)} \\\\&= 14.5\times10^{7} \\\\&= 1.45\times10^{8} .\end{align*}