Since you know that point Y and point Z are equal distance form point F, you will need to know the distance between point Y, -1, and the distance between point X, -7. So, the total distance, after subtracting -1 from -7, is -6. So, you will then subtract another -6 from -7, to get -13, which is the coordinate of point Z.
48 girls are there. Given that there is a ratio of boys to girls of 7:8. Then divide 42 boys by 7 boys which equals 6. After, multiply 6 by 8 girls equals 48 girls.
