In Robert Recorde's Grounde of Artes (1541), an arithmetic text for algorists and abacists, Recorde gave an rule for multiplying two one-digit numbers greater than 6. Here is the rule: first subtract each number from 10. The product of the two differences you get is the units digit in the product of the original numbers, and if you subtract one of the differences from the other original number, you get the tens digit in the product of the original numbers. A) Show two examples of this method.
B) Prove that it works.