the ratio of boys to girls is 3:1
so divide your total amount of students (236) by 4.
That will give you 59. That represents the amount of girls.
If you multiply 59 by 3 (because there ratio is 3:1) you will get the amount of boys.
59*3=177
So to sum up, the ratio of boys to girls is 3:1, making 177 boys taking classes and 59 girls taking classes.