Rachel saved $200 and spends $25 each week. Roy just started saving $15 per week. At what week will

Rachel saved $200 and spends $25 each week. Roy just started saving $15 per week. At what week will they have the same amount?

Let Rachel's account value R(w) where w is the number of weeks be:
R(w) = 200 - 25w <-- We subtract -25w because she spends it every week, decreasing her balance.

Let Roy's account value R(w) where w is the number of weeks be:
R(w) = 15w

Set them equal to each other:
200 - 25w = 15w

To solve this equation, we type it into our search engine and get:
w = 5