Answer
$$14 e^{-0.2079\ t}$$
Work Step by Step
Recall the property $(a^m)^n=a^{mn}$, so the equation can be rewritten as $$Q=14(0.862)^{1.4 t}=14 (0.8123)^t=14 (e^{\ln 0.8123} )^t ~~~~(1)$$
Evaluating $\ln 0.8123$ yields $-0.2079$.
Therefore, the equation (1) can be written as $Q=14 (e^{\ln 0.8123} )^t=14 e^{-0.2079\ t}$