Mail rows

How can i use this class get_total_ex_tax in my E-Mail Template.

I have this function in class-wc-order.php

if ( $total_ex_tax = $this->get_total_ex_tax() )
$total_rows[‘test’] = array(
‘label’ => __( ‘test’, ‘woocommerce’ ),
‘value’ => get_total_ex_tax()
);

http://ww.wp.xz.cn/extend/plugins/woocommerce/