Added Grade.java with grading methods

Author: TusharKumarRoy

Grade.java

@@ -0,0 +1,8 @@
+public class Grade {
+    public String getGrade(int marks) {
+        if (marks >= 90) return "A";
+        if (marks >= 75) return "B";
+        if (marks >= 60) return "C";
+        return "F";
+    }
+}