Suppouse the initial amount of money of Megan is C, if she withdraws $22.50 each day from her account for a week, and you consider variable x as number of days on a week, then, the following equation can describe the given situation:
y = C -22.50x 0 ≤ x ≤ 7
As you can notice, each day (tah is, for each value of x), the initial amount of money C is decreased by 22.50x.