Tabitha is raising money for the American Cancer Society. To raise money, she takes donations from family and friends and does a "walk-a-thon" where she will earn money for each mile she walks. She collects $18 for every mile that she walked. In addition, her grandmother gave her a $72 donation. She collected $234 in total. Write and solve an equation to find the number of miles, m, Tabitha walked. Explain your equation in the context of this equation and validate your result.