hello!
Let the number be n.
Now, "seven less than a number" means we subtract 7:-
n-7
This expression is equal to 18:-
![\sf{n-7=18}](https://img.qammunity.org/2022/formulas/mathematics/high-school/58h92x6ptrfc4am5umc3uug3ityno9p7y4.png)
![\mathcal{SOLUTION:-}](https://img.qammunity.org/2022/formulas/mathematics/high-school/k9pymbxvw6gkdx781pdjsjd7f3s32pkdzn.png)
![\bigstar{\boxed{\pmb{n=25}}}](https://img.qammunity.org/2022/formulas/mathematics/high-school/9pi9986mvkslxt4zpoizeyzn5wg6bra6iu.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 :)