A certain ore yields an average of 64 % iron. how much ore is needed to obtain 896 lb of iron?

In this case, the ore yield 64% iron and you need 896 lb of iron. From this description you can get an equation like this:

Iron = iron ore mass * 64%

Then, to get 896 of iron the calculation should be:

Iron = iron ore mass * 64%

896 lb = iron ore mass * 0.64

iron ore mass = 896 lb / 0.64 = 1400lb