What does it mean to have a shortage of goods?

Palmer frosted flakes company offers its customers a pottery cereal bowl if they send in 3 boxtops from palmer frosted flakes boxes and $1. the company estimates that 60% of the boxtops will be redeemed. in 2012, the company sold 675,000 boxes of frosted flakes and customers redeemed 330,000 boxtops receiving 110,000 bowls. if the bowls cost palmer company $3 each, how much liability for outstanding premiums should be recorded at the end of 2012?