Roman Number Wordplay/9 from 6, 10 from 9, 50 from 40

Puzzle

If from six ye take nine, and from nine ye take ten

(Ye youths, now the mystery explain),

And if fifty from forty be taken, there then,

Shall just half a dozen remain.

$\ds \mathtt {SIX}$

$\ds $

$\ds \text {minus} \ \ $

$\ds \mathtt {IX}$

$\ds $

$9$ expressed in Roman numerals

$\ds \text {leaves} \ \ $

$\ds \mathtt {S}$

$\ds $

$\ds \mathtt {IX}$

$\ds $

$9$ expressed in Roman numerals

$\ds \text {minus} \ \ $

$\ds \mathtt X$

$\ds $

$10$ expressed in Roman numerals

$\ds \text {leaves} \ \ $

$\ds \mathtt {I}$

$\ds $

$\ds \mathtt {XL}$

$\ds $

$40$ expressed in Roman numerals

$\ds \text {minus} \ \ $

$\ds \mathtt L$

$\ds $

$50$ expressed in Roman numerals

$\ds \text {leaves} \ \ $

$\ds \mathtt X$

$\ds $

Putting them together gives:

$\mathtt{SIX}$