Cloud City 4-2 is the second level of Cloud City. To pass this level with three stars, you should pop all pigs and score at least 78,000 points.
Getting 3 stars is extremely difficult since target score is very high. You need to destroy almost blocks for three stars if you use two birds. Using three birds never get three stars.
Send Chewie high, the steam will push him horizontally into the first tower. Sending the next Chewie more horizontally to begin with, the steam will lift him into the remaining glass blocks. With a massive amount of luck, it should makes enough points for three stars.