H= 1/2r + 3b - 1/4. solve for r that equals to 2h/3b + 1/4 right?

Ahealth-food producer has 250 samples of a new snack to distribute in the mall. the producer has to keep at least 50 samples for display in the health food for the product launch. how long will the samples last if consumers are taking the samples at a rate of 25 every hour