An urgent need to solve an alloy of lead and tin weighing 40 kg contains 20% tin

An urgent need to solve an alloy of lead and tin weighing 40 kg contains 20% tin. How much tin needs to be added to the alloy to make it 64% lead.

100-64 = 32 (%) – tin will be in a new alloy.
20% – 0.2; 32% – 0.32;
Let’s make the proportion:
0.2 / 8 = 0.32 / x;
x = 8 * 0.32 / 0.2;
x = 12.8 (kg) – tin is 32% in the new alloy;
12.8-8 = 4.8 (kg) – tin must be added to the alloy so that the lead in it becomes 64%.
Answer: 4.8 kg.