Question A: 
Which team has a greater percent of left-handed batters?
Solution:
Sierra's team has a greater percentage of left-handed batsmen than Aubrey. Below is the work.
Aubrey's team: 5/25 left-handed batsmen
- => 5/25 x 100 = 1/5 x 100
 - => 20%
 
Sierra's team: 7/28 left-handed batsmen
- => 7/28 x 100
 - => 1/4 x 100
 - => 25%
 
Hence, Sierra's team has a greater percentage of left-handed batsmen than Aubrey. 
Question B: 
What percent of the players on Sierra's team bat left-handed?
Solution:
25% of the players on Sierra's team are left-handed batsmen. 
Below is the work.
- Sierra's team: 7/28 left-handed batsmen
 - => 7/28 x 100
 - => 1/4 x 100
 - => 25%
 
Hence, 25% of the players on Sierra's team are left-handed batsmen.