David baked some muffins. He gave 1/8 of the muffins to his siblings and 15 muffins to his colleagues. He was left with 4/5 of the muffins. He packed the remaining muffins equally into 20 boxes. How many muffins were packed into each box?

x - x/8 - 15 = 4x/5

x = 200
(4/5 * 200)/20 = 8