In this final chapter of the trilogy, the four young wellies find themselves taking on the ultimate task of helping River overcome her fear of math.

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Coming together with the rest of the hallway crew, they devise a plan to help the little girl at the center of their universe see that her dread of numbers is far from the end of the world.

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But when it comes to the crunch, will they flunk their greatest challenge yet? Or will they figure it all out in the end…