Answer
$x = -\dfrac{\ln{1.2}}{\ln{8}} \approx -0.088$
Work Step by Step
Take the natural logarithm of both sides to obtain:
$\ln{(8^{-x})} = \ln{1.2}$
Use the rule $\ln{a^x} = x \cdot \ln{a}$ to obtain:
$-x\cdot \ln{8} = \ln{1.2}$
Divide both sides of the equation by $-\ln{8}$ to obtain:
$\dfrac{-x\cdot \ln{8}}{-\ln{8}}=\dfrac{\ln{1.2}}{-\ln{8}}
\\x = -\dfrac{\ln{1.2}}{\ln{8}}
\\x \approx -0.088$
