Given,
Total money needed = 225
Money already Marie has = 85
Marie per day Income = 20
Let it take x days for Marie to have enough money to buy the prom dress.
We can say:
Total Money = Money Marie already has + per day income
Using the given information, we can craft an inequality shown below:
This means "85 already have plus 20 per day will need to be atleast 225".
Now, we can do algebra and solve for x. Steps are shown below:
Thus, Marie needs 7 days more to have enough money to buy the prom dress.