We know that the ration/percentage that brass is made of remains the same no matter what the weight is;
Therefore, 48 ounces are 80% of the trumpet.
48/80= 0.6 ounce per percent of the zinc (I divided the weight by the percent)
0.6 ounces × 20%= 12 ounces
Therefore, there are 12 ouches of zinc in Henri's trumpet.
Hope I helped :)
