I think the author made a typo, and they actually meant to refer to 2.92, not 2.29. The table preceding the part mentioning 2.29 only includes 2.92. And 2.29 doesn't include the text "This is not easy!”, whereas 2.92 does.
That makes a lot more sense. It also matches the times they record for the exercise. For context, 2.92 is:
> Exercise 2.92. By imposing an ordering on variables, extend the polynomial package so that addition and multiplication of polynomials works for polynomials in different variables. (This is not easy!)
2.29 is what I described in my other comment, it's a pair of functions walking a binary tree with conditional logic based on if it's an interior or exterior node, returning either a sum or a true/false value. Which is not hard at all and their time was only 83 minutes. Versus their claimed time of 2400 minutes for 2.92.
