We can not really tell in this question as you dont know the equation that is being used for the domain and range relationship but overall one should know that:
The set of values of the independent variable(s) for which a function or relation is defined as the domain of a function. Typically, this is the set of x-values that give rise to real y-values.
The range of a function is the complete set of all possible resulting values of the dependent variable (y, usually), after we have substituted the domain.
So there is 3:5 right, so 20 divided by 5 equals 4, there are four 5's in 20. Then 4 multiplied by 3 equals 12. So there are 12 students that has BROWN EYES.
