1 ÷ 45% = 20/9, so the total number of sweets is 20 times that of 9% butterscotch.

1 ÷ 25% = 4. Later, the total number of sweets was four times that of toffee.

16 ÷ 4-20/9 ÷ =16 ÷16/9 = 9 pieces. There are nine pieces of toffee.

9× 20/9 = 20 pieces. It turns out that the number of sweets in this pile is 20.