Let x represent number of miles.
We have been given that Melissa's mother will donate $2 for each mile that Melissa walks. So amount donated by Melissa's mother for x miles would be
.
We are also told that her will donate $10 for Melissa's participation. The total amount of money donated by Melissa's mother will be participation amount plus amount donated for x miles.
.
To find amount of her mother's donation, we will substitute
in our equation.



Therefore, the amount of Melissa's mother's donation would be $40.