In text box changed event of monthly column, you can write code to calculate yearly column value as:
Private void datagridview_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
e.Control.TextChanged +=new EventHandler(txtMonthly_TextChanged);
cntObject=e.Control;
cntObject.TextChanged +=txtMonthly_TextChanged;
}
Private void txtMonthly_TextChanged(object sender, EventArgs e)
{
if(cntObject.Text!=string.Empty)
{
txtYearly.Text=int.Parse(cntObject.Text)*12;
}
}