Let iron = x
There is 1.5 times the amount of zinc that there is iron, so you get zinc = 1.5x
There is 3 times as much copper as there is zinc, so 1.5 x 3 = 4.5, so copper equals 4.5x
Now all three need to equal the total weight of 210:
X + 1.5x + 4.5x = 210
Simplify:
7x = 210
Divide both sides by 7:
x = 210 /7
x = 30
Now you have a value for x, you can solve for the amount of each material.
Iron = x = 30 g
Zinc = 1.5x = 1.5(30) = 45 g
Copper = 4.5x = 4.5(30) = 135g
There is 45 g of zinc.