Chapter 9 - Test - Page 599: 15

$-1.53$

Using the properties of logarithms and the given values of logarithmic expressions, then, \begin{array}{l} \log_b \dfrac{3}{25} \\\\= \log_b 3-\log_b 25 \\\\= \log_b 3-\log_b 5^2 \\\\= \log_b 3-2\log_b 5 \\\\= 0.79-2(1.16) \\\\= -1.53 .\end{array}