The table above shows the number of students in three 11th grade math classes taught by Mr. Mehta at South High School. The ratio of boys to girls in Class 1 is 5 to 4. The ratio of boys to girls in Class 2 is 1 to 1. The ratio of boys to girls in Class 3 is 4 to 7. How many more girls than boys does Mr. Mehta teach in his three 11th grade math classes?