ANSWER
[tex]t=-\frac{r}{4}[/tex]EXPLANATION
We want to solve the given equation for t:
[tex]8t-r=12t[/tex]To do this, separate the variables of the equation and simplify it:
[tex]\begin{gathered} 8t-12t=r \\ -4t=r \\ t=\frac{r}{-4} \\ t=-\frac{r}{4} \end{gathered}[/tex]That is the solution to the equation for t.