$$\begin{aligned} & \sin x=-\frac{3}{5} \text { where } \pi < x < \frac{3 \pi}{2} \\ & \qquad \tan x=\frac{3}{4}, \cos x=\frac{-4}{5} \\ & \therefore 80\left(\tan ^2 x-\cos x\right) \\ & =80\left(\frac{9}{16}+\frac{4}{5}\right) \\ & =80\left(\frac{45+64}{80}\right) \\ & =109 \end{aligned}$$