An alloy contains tin, copper and silver in the ratio $7: 5: 3$. If there is $48 \mathrm{~g}$ of copper, how much tin and silver are needed to make the alloy? (4 marks)

Step 1 ：Given the ratio of tin, copper, and silver as \(7:5:3\) and there are \(48\mathrm{~g}\) of copper.

Step 2 ：Find the total parts in the alloy: \(7+5+3=15\).

Step 3 ：Find the value of one part: \(\frac{48}{5}=9.6\).

Step 4 ：Find the amount of tin needed: \(7\times9.6=67.2\mathrm{~g}\).

Step 5 ：Find the amount of silver needed: \(3\times9.6=28.8\mathrm{~g}\).

Step 6 ：\(\boxed{\text{To make the alloy, 67.2g of tin and 28.8g of silver are needed.}}\)