Creating Synthetic Cash - CFAI Version 2

In the last question of this test, we are required to convert 75 million in the following portfolio: 100% mid-cap equities: Beta = 1.2 To cash using this contract: US Mid-cap equity contract: Beta = 1.29, price = 2350, multiplier = 100 The CFAI text specifies that (page 111 - volume 5) to use the traditional synthetic cash equation “… The stock portfolio, however, has to be identical to the index. It cannot have a different beta. The other formula, which reduces beta to zero, is more general and can be used to eliminate systematic risk on any portfolio” The solution uses the synthetic cash formula. Any idea what’s going on ?