McDonald's sells 5 times as many coffees as Burger King. The difference in sales on Monday between the two was 20 cups. How many cups of coffee did each restaurant sell?

Step 1 ：Let's denote the number of coffees sold by Burger King as \(x\). Then, the number of coffees sold by McDonald's is \(5x\). The difference between the two is 20 cups, so we can set up the equation \(5x - x = 20\).

Step 2 ：Solving the equation \(4x = 20\), we find that \(x = 5\).

Step 3 ：This means Burger King sold \(5\) cups of coffee.

Step 4 ：Since McDonald's sells 5 times as many coffees as Burger King, McDonald's sold \(5 * 5 = 25\) cups of coffee.

Step 5 ：Final Answer: Burger King sold \(\boxed{5}\) cups of coffee and McDonald's sold \(\boxed{25}\) cups of coffee.