At Jim's super sales club store.. boxes of breakfast cereal weigh 2 lbs 10 ounces and cost $4.20 each. At sues grocery store bxs of breakfast cereal weigh 1 lb 9 oz and costs $3.75. What is the difference in the cost of the cereal in cents per ounce at the two stores.

Simple math. Convert everything to ounces and divide into cost.