Suppose freshman year, first semester i get a 3.25 gpa, and the last semester of freshman year i get a 4.0. assume i get a 4.0 the rest of my high school career.. what gpa can i end with? and will it be a good gpa ? ?

It depends on how many semesters you have
in my school ther are 2 symesters so
to find the gpa you average

4 years in hight school
2 ysmpersers each
4 times 2=8
so we do
total gpa=3.25+4+4+4+4+4+4+4=31.25
to take the average, we divide by number of symesters
31.25/8=3.9
average gpa is 3.9 which is decent
sometimes you need over 4.0 so take some AP or honors or weighted classes

Just tell koda to adjust the number of shapes himself.