Hi!
We know the amount needed to make 8 pancakes. Dan wants to make 12 pancakes. 12/8 = 1,5, that's the ratio, we need to multiply each ingredient with 1.5 and we will get the amount needed to make 12 pancakes.
240 * 1,5 = 360 g of plain flour
2 * 1,5 = 3 eggs
600 * 1,5 = 900 ml of milk
Hope this helps!