ANSWER
Ruth, since she has a higher z-score.
Step-by-step explanation
Given a mean μ and a standard deviation σ, the z-score of a measure x is:

For Ruth, her GPA is x = 3.7. Her school has a mean GPA of 3.0 and a standard deviation of 0.4. The z-score is:

For William, his GPA is x = 3.75. His school has a mean GPA of 3.2 and a standard deviation of 0.5. His z-score is:

Since Ruth has a higher z-score, her GPA is higher when compared to each of their schools.