For each of the 3 working steps I tried to explain the reasoning as best as I could and also included some illustration by the side, hopefully it helps you visualize and understand better! Also would like to add that this method worked because 2 5cent coins made up 1 10cent coin (and therefore 2 5cent coins replaced/became 1 10cent coin). This method would also work for another question involving 10c and 20c coins OR 50c and $1 coins.

Hope it helps :)