Sterling silver is an alloy of silver containing 92.5% by mass of silver
and 7.5% by mass of other metals, to keep it from tarnishing.

Let x = the number of lbs. of sterling silver that can be made

Then the 80 lbs. of silver must be 92.5% of the x lbs of sterling silver.

So 

   92.5% of x = 80
       0.925x = 80
            x = 
            x = 86.48548649 lbs of sterling silver (round that off as 
you were told).

Edwin