Issued as a cumulative or non-cumulative L/C, the former allows for unused credit amounts to rollover into subsequent periods while the latter maintains a fixed amount of credit available each period.
average atomic mass of magnesium is 24.3 g/mole so 24.3 X 1.56 X1021 / 6.02 X1023 = .063 grams.
Magnesium (Mg) is the lightest of all metals, being about two-thirds lighter than aluminium. Magnesium is non-toxic, non-magnetic, has high-impact strength and is resistant to denting. Magnesium is too reactive to occur in nature as an element, but its compounds are common. At 2.5%, magnesium is the eighth most abundant element in the earth's crust. It is the third most abundant element in sea water which averages about 0.13% magnesium by weight.