Supergirl "World's Finest" (March 28, 2016) happened during The Flash "Versus Zoom" (April 19, 2016). CBS and The CW didn't coordinate the episodes to happen in the same week. So, one can watch the first few minutes of "Versus Zoom" then go over to "World's Finest" and watch it completely then go back to "Versus Zoom".
Supergirl "World's Finest" (March 28, 2016) happened during The Flash "Versus Zoom" (April 19, 2016). CBS and The CW didn't coordinate the episodes to happen in the same week. So, one can watch the first few minutes of "Versus Zoom" then go over to "World's Finest" and watch it completely then go back to "Versus Zoom".