Aling Lara has a 2-pan scale and a set

of 4 steel weights. She claims that she

can weigh out any whole number of

ounces up to 40 ounces using just these

weights, and she's right. What is the

weight of each brass weight? (Note that

you can put weights on either pan of the

scale, so both adding and subtracting are

possible. ​