Based upon the molarities of the standardized hcl and standardized naoh, and the volumes of each added to analyze the antacid samples, calculate the millimoles of hcl needed to neutralize the tablet per milligram of sample.

average molarity hcl: 0.4548
average molarity nacl: 0.1048
vol hcl(ml): 14.10
vol nacl(ml): 14.60
mass tablet: 1.333g
mass antacid: 0.613

The difference between the moles of acid and moles of alkali will indicate the moles of acid that reacted with the antacid tablets. Generally, the moles are calculated using:

Moles = Molarity * liters

But if we are calculating millimoles, we may use mL. Using this:

Moles reacted with antacid = moles of HCl - moles of NaOH
Moles reacted = 0.4548 * 14.1 - 0.1048 * 14.6
Moles reacted = 4.88 millimoles

The mass of the tablet was 1.333 grams = 1333  mg

Millimoles of acid per mg tablet = 4.88/1333

There are about 0.0037 millimoles reacting per milligram of tablet.