We are given the following expression:
![8x-5y](https://img.qammunity.org/2023/formulas/mathematics/college/thd3zvshifn0s3wqhe2nkarqlkgrzczffy.png)
We are asked to evaluate the expression at;
![\begin{gathered} x=4 \\ y=-9 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/mugbvp8yvw5j7ip8snbczv3g3smih60dq6.png)
To determine the numerical value of the expression at the given points we will substitute the values, like this:
![8(4)-5(-9)](https://img.qammunity.org/2023/formulas/mathematics/college/ltemv4x4i0dboph81w251xhvuy17ej7rs6.png)
Now, we solve the products:
![8(4)-5(-9)=32+45](https://img.qammunity.org/2023/formulas/mathematics/college/3xvrfr4dxrpigox0cenjpbsd4xnhnwahf8.png)
Now, we solve the addition:
![32+45=77](https://img.qammunity.org/2023/formulas/mathematics/college/bmskjgu9ufkl4wu8c2jljyrm3jd1egqwvs.png)
Therefore, the value of the expression is 77.