i understood that rapido meant rapid and that rapidamente meant quickly. rapid is an adjective - rapidly is an adverb. I used the words as shown, but still got it wrong - maybe a different sentence would alleviate this problem for others.

Yeah I find this very strange, why are we suddenly being introduced to adverbs? It's confusing because it's an adjective being used as an adverb, I don't think this is a useful sentence at all.