A manufacturer of briquets has a contract to make briquets for barbecuing that are guaranteed to not contain over 10% moisture or 10% ash. The basic material they use has the analysis: moisture 12.4 %, volatile material 16.6 %, carbon 57.5 % and ash 13.5 %.

To meet the specifications (at their limits), they plan to mix with the base material a certain amount of petroleum coke that has the analysis: volatile material 8.2 %, carbon 88.7 % and moisture 3.1 %.

How much petroleum coke must be added per 100 lb of the base material?