So you got it.
Applying percentahes is multiplication rather than division.
So if 58% of the ore is iron oxide and you have 10,000 kg of ore you have
0.58 * 10000 kg = 5800 kg of iron oxide.
Any questions?
And if 70% of iron oxide is iron, then the iron in 5800 kg of iron oxide is
0.70 * 5800 kg = 7 * 580 = 4050 kg of iron.