3.17 GPA is equivalent to B+ Letter Grade.
Your GPA is the total of all your course grades throughout your high school career divided by the total number of credits. Most high schools (and colleges) report grades on a 4.0 point scale.
The chart below shows how letter grades translate.
Is Your GPA Holding You Back? | Prep | The Princeton Review via kwout
To convert GPA to letter grade, you can use RapidTables GPA to letter grade conversion calculator.
Check out Tips for Improving Your Grade Point Average, shared by University of Maine at Farmington.