Final answer:
A block of brass that contains 15 kg of zinc also contains 35 kg of copper.
Step-by-step explanation:
In a brass alloy containing 30% zinc, we can assume that the remaining 70% is copper. So if a block of brass contains 15 kg of zinc, we can calculate the amount of copper in the block as follows:
Copper content = 70% of the total mass of the block
Copper content = 70% x Total mass of the block
Copper content = 70% x (Mass of zinc + Mass of copper)
Copper content = 70% x (15 kg + Mass of copper)
To solve for the mass of copper, we can set up the equation:
0.7 x (15 kg + Mass of copper) = Mass of copper
0.7 x 15 kg + 0.7 x Mass of copper = Mass of copper
10.5 kg + 0.7 x Mass of copper = Mass of copper
0.3 x Mass of copper = 10.5 kg
Mass of copper = 10.5 kg / 0.3
Mass of copper = 35 kg
Therefore, the block of brass contains 35 kg of copper.