If the sales manager goes through 3 bottles of antacid every day, we can calculate how long the gross will last by dividing the total number of bottles in the gross by the number of bottles used per day.
Number of bottles in a gross = 144
Number of bottles used per day = 3
Days the gross will last = 144 bottles / 3 bottles per day = 48 days.
Therefore, the gross of antacid bottles will last the sales manager for approximately 48 days.