What is the highest eligible free rate for K-12 students in the schools in Alameda County?
Eligible free rate for K-12 = `Free Meal Count (K-12)` / `Enrollment (K-12)`
SELECT `Free Meal Count (K-12)` / `Enrollment (K-12)` FROM frpm WHERE `County Name` = 'Alameda' ORDER BY (CAST(`Free Meal Count (K-12)` AS REAL) / `Enrollment (K-12)`) DESC LIMIT 1