All you have to do to get the result is to divide their total weight (3/8 lb) by 6 magazines.
3/8 : 6
Dividing fractions is multiplying the first fraction by the inverse of the second fraction, so as far as 6 is equal to 6/1, the calculation will look as it follows:
3/8 * 1/6 = 3/48 lb
You can simplify it to 1/16 lb.
