insertion decimal into database

test.Text = "t" + decimalsh.ElementAt(i).ToString(); output 2,75 i want to insert decimal list into database

when i test can not insert if i get 2,78 but if  2 i insert without problem.
qkoef = "insert into dbo.koeficienti(kofh,kofx,kofa) VALUES('2,78','2','2')";
in database kofh datatype is decimal(5, 2)