$\max 6t_1 + 4t_2$
$-t_1 + t_2 \leq 6$
$t_1 - t_2 \leq 1$
$t_1 - 2t_2 \leq 8$
$t_1, t_2 \geq 0$
If you have been taught the relationship between the primal and dual forms of a linear program then you can take advantage of the fact that if the primal is unbounded then the dual is infeasible.
The dual constraints can be written as:
$-y_1 + y_2 +y_3 \ge 6$
$y_1-y_2-2y_3 \ge 4$
$y_1 \ge 0$, $y_2 \ge 0$ and $y_3 \ge 0$.
Adding up the first two inequalities we get:
$-y_3 \ge 10$ which is incompatible with the condition that $y_3 \ge 0$.
Thus, the dual constraints are infeasible which implies that the primal is unbounded.