Which pop star wrote Fifth Harmony's hit 'Sledgehammer'?

There's no doubt that these ladies are "Worth It." But before Fifth Harmony perform their hits live Friday on the TODAY plaza, we're testing their fans with this trivia question.

Tune in tomorrow to find out the correct answer. And whether you're watching the concert from home or in person, share your pics and Tweets with the hashtag #FifthHarmonyTODAY.