What would my gpa be of i had five a's and one b-?

7.5 tablespoons of salt

Explanation:

The old aquarium had 20 gallons of water while the new aquarium had 50 gallons of water.

If 20 gallons of water required 3 tablespoons of salt

50 gallons of water will require: 50 x 3/20 = 7.5 tablespoons of salt

Hence, 7.5 tablespoons of salt should be added to her new aquarium.