hello!
In order to simplify this expression, we need to use the Distributive property, which states the following:-
![\bigstar{\boxed{\pmb{a(b+c)=ab+ac}}}](https://img.qammunity.org/2023/formulas/mathematics/high-school/ik3urizx31gwfmv3xk3ie8q1hp1j7ltgjr.png)
Distribute:-
![\sf{-3(4a-5b)}](https://img.qammunity.org/2023/formulas/mathematics/high-school/ezwstpct1zcjyd4hrvi0mf6ajiqqokk9v6.png)
Multiply -3 times the terms inside the parentheses:-
![\bigstar{\boxed{\pmb{-12a+15b}}}](https://img.qammunity.org/2023/formulas/mathematics/high-school/fj1sgtribh9en1jz0m7a65tfparg4cg6jr.png)
note:-
Hope everything is clear; if you need any clarification/explanation, kindly let me know, and I will comment and/or edit my answer :)