How can I perform operation in SQL query?

How can I perform operation in SQL query?

Im making a command that will compute for fine if the books overdue. this
is my code
if (duedate.Value < DateTime.Now)
{
cmd.CommandText = ("UPDATE Penalty SET Penalty = '"+
(dateTimePicker1.Text - duedate.Value)*50 +"' WHERE Title =
'" + textBox3.Text + "'");
This code is not running because it has an error on dateTimePicker1.Text -
duedate.Value)