Arithmetic Mistake

I am a Rothbardian. To the bone. I understand and would defend the axiomatic-deductive logic of Man Economy and State any day. I just want to warn you, that if you want to do the same, just be aware that there is an arithmetic error in Chapter 9:

The lower stage bought its factors for 118 ounces and sold the product for 140 ounces, making a 29-percent return