Show the Trachtenberg ×11 rule: "add the neighbour."

Prepend a zero, then each answer digit = that digit + the digit to its right, carrying as usual.

For 633 × 11, write it as 0633 and add each digit to its right neighbour:

• 3 + (nothing) = 3
• 3 + 3 = 6
• 6 + 3 = 9
• 0 + 6 = 6

→ 6963. Check: 633 × 11 = 6963. ✓ It's the same "insert the sum" idea from Mission 2, formalised as a digit rule. (Trachtenberg's ×12 rule is the cousin: double each digit and add the neighbour.)