艾莉（Elly）、内森（Nathan）和特伦斯（Terence）每人拥有的镇纸数量相同。艾莉有 9 个金属镇纸和一些木质镇纸。艾莉的镇纸总质量为 44.7 g。特伦斯只有木质镇纸。艾莉发现她的镇纸总质量比特伦斯的镇纸总质量多 7.2 g。内森有 4 个金属镇纸和一些木质镇纸。求内森的镇纸总质量。 答：___ g

1. Find the difference in mass between 1 metal weight and 1 wooden weight.

Since Elly and Terence have the same total number of weights, but Elly has $9$ metal weights while Terence has only wooden weights, the $7.2\text{ g}$ difference is due to $9$ metal weights replacing $9$ wooden weights.
Difference between $9$ metal and $9$ wooden weights $= 7.2\text{ g}$
Difference between $1$ metal and $1$ wooden weight $= 7.2 \div 9 = 0.8\text{ g}$

2. Find the total mass of Terence's weights.

Terence's total mass $= 44.7 - 7.2 = 37.5\text{ g}$

3. Calculate the total mass of Nathan's weights.

Nathan has the same total number of weights as Terence, but with $4$ metal weights instead of wooden ones.
Nathan's total mass $= 37.5 + (4 \times 0.8) = 37.5 + 3.2 = 40.7\text{ g}$