private void ExtraClassesActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_ExtraClassesActionPerformed
        // TODO add your handling code here:
        this.setVisible(false);
        ExtraClassesMaths ecc = new ExtraClassesMaths();
        ecc.setVisible(true);
    }//GEN-LAST:event_ExtraClassesActionPerformed