1. **State the problem:** Given $t=8$ and $u=9$, evaluate the expression (expression not provided, so assuming a general evaluation of $t$ and $u$). 2. **Identify the expression:** Since no specific expression is given, we can only substitute the values of $t$ and $u$ if an expression is provided. 3. **Substitution:** For any expression involving $t$ and $u$, replace $t$ with 8 and $u$ with 9. 4. **Evaluation:** Calculate the numerical value after substitution. Since no expression is provided, no further evaluation can be done.