10 - 4 = 6
2 * 10 = 20
(2 * 10) - (2 * (10 - 4)) = 8

As yf žou wol multiply
2 be 4. loke how mony vnitees ben by-twene že quych is že more
nounbre, & be-twene ten. Certen žere wel be vj vnitees by-twene 4
& ten. yf žou reken žere with že ten že vnite, as žou may se. so
mony tymes take 2. out of his decuple, že quych is 20. for 20 is že
decuple of 2, 10 is že decuple of 1, 30 is že decuple of 3, 40 is že
decuple of 4, And že ožer digetes til žou come to ten; & whan žou
hast y-take so mony tymes 2 out of twenty, že quych is sex tymes,
žou schal leue 8
- http://www.pgdp.net/phpBB2/viewtopic.php?p=189148#189148
Currently in P2, The Earliest Arithmetics in English; 
the specific text is "The Crafte of Nombrynge" from the 15th century.