In the expression 15+n, the sum of number 15 and variable n is given.
Consider option 1,
If Nick took n cookies from the plate consist of 15 cookies, then expression for the remaining cookies is,
![15-n](https://img.qammunity.org/2023/formulas/mathematics/college/1jzv93e55b70w3dtiiu3ba435z1ms3evh9.png)
Consider option 2,
The expression for total cost of n CD's with each CD cost $15 is,
![15n](https://img.qammunity.org/2023/formulas/mathematics/college/icm5s9nel504ehwi3ilb21erb3tkxqerat.png)
Consider option 3,
The expression for total number of pages read by Mathew in n days , with 15 pages every day is,
![15n](https://img.qammunity.org/2023/formulas/mathematics/college/icm5s9nel504ehwi3ilb21erb3tkxqerat.png)
Consider the option 4,
The total number of students with 15 females and n males is,
![15+n](https://img.qammunity.org/2023/formulas/mathematics/college/ebff2lsy82xflvjswth9upxm5cfi6mgpwa.png)
So last option is correct for the expresion 15+n.