The more stable chair is the second one.
Work Step by Step
1. Draw both chairs with the substituents. - We've learned how to do this on the previous sections. 2. Find the largest substituent. - In this case the isopropyl is the largest (The one with 3 carbons). 3. Now, identify the chair where the largest group is in the equatorial position. - In the second chair, the isopropyl is in the equatorial position, so it is the more stable.