19/20, fooled by Mattel (and guessed lucky on the other all caps texts). My heuristic was to look at the a, c, e, g, and s, if present in lowercase: are the ends of those characters horizontal (Helvetica) or at an angle (Arial).
I also got all except Mattel, despite not really using either typeface all that much. Lowercase 't' was also a dead giveaway in a lot of cases. I also noticed that the Helvetica answers seemed to have a slightly heavier weight, which really helped for the all-caps examples.
Ultimately, the Helvetica versions "felt right", and that probably contributed to my lucky guesses. A more challenging test would be to compare samples not associated with well-known brands.