la tasa is rate. impuesto is tax
‘tasa’ can mean either one, or “fee”, but ‘impuesto’ is certainly a more common word for tax.
This one seems a bit cruel to create a listening question out of, since "taza" and "tasa" sound identical in Latin American Spanish.
Agreed. More to the point, they're homophonous in the dialect of the speaker. In the listening test, both are correct. Please report it using the ‘Report a Problem’ link if ‘taza’ is rejected.