@Michael_B, this one me. Not sure what to do here other than wave. 
Does the Q give mass or moles of the solution?
The passage gives the mass, and the question the molar mass, for the compound in question (BaSO4).
Molar mass is g/mol but the nid gives the equation for molarity (mol/L). Browsing through the deck, doesn’t seem like we have a card for molar mass yet. Definitely would be something to add for a new note suggestion