If haylee got a gpa average of 2.3 freshman and sophomore year but got a 4.0 junior and senior year, what is her average gpa for all four years

Let's use mean to find this. Let's add 2.3 and 4 each twice, one number per year.
2.3+2.3+4+4=12.6
Now divide 12.6 by four since there are 4 numbers. 
12.6/4=3.15.
Haylee's average GPA is 3.15.