Complex sentence: Sharpay is enraged upon learning that Gabriella is working as one of the lifeguards but is unable to get her fired so she orders Fulton to give them difficult tasks so they would be best to quit.
Split into simpler sentences: Sharpay is enraged upon learning that Gabriella is working as one of the lifeguards, but is unable to get her fired. So she orders Fulton to give them difficult tasks so they would be best to quit.