They list Imidan at 2.43 grams per tsp. There is roughly 454 grams in a pound.
454 / 2.43 = 187 tsp per pound. 187/2.5 = 74.8 gallons of spray per pound. 74.8 * 5 = 374 gallons of spray.
Not sure why Google is telling you 1 pound = 96 tsp. Its a weight to volume conversion, every material can have a different density thus a different variable.