I have tried dividing the 0.75g of the g/mol of the Alka-Seltzer (citric acid and sodium bicarbonate) which is 276.0g/mol(?).
Well for starters this sentence doesn't make sense. Moreover, Alka-Seltzer is a complex mixture of unspecified formulation, so it doesn't have a molecular weight. You are given a rate of some kind for Alka-Seltzer "dissolving", but you don't know the composition of Alka-Seltzer, and in any case the rate isn't really defined. Different components in Alka-Seltzer likely dissolve at different rates. Finally, the question gives some confusing and ambiguous meaning of the word "dissolve". Does the question mean "reacts according to the given chemical equation" or does it mean dissolve in the strict chemical sense?
Is this the exact wording of the entire question? Because as it's given here it really makes very little sense.