Why ZZ = (10×Z)+Z when Z = 4

Question

I started to learn mathematical fundamentals course at brilliant.org and there is a puzzle

Maybe is too late or I just don't get it, why is

ZZ = (10×Z)+Z

and how they get this equation from the question ? Because the formula does not even fit, but leads to a successful solution, I'm confused.

4 x 4 != (10 x 4) + 4 
16 != 44

Answer 1

When they write "ZZ", it means a number like 33, 44, 55, etc. where it's just two digits repeated.

Writing two letters together in elementary algebra implies multiplication. But in our base-ten system (ones, tens, hundreds, thousands, etc.), that means TEN times the digit in the TENS digit, plus ONE times the digit in the ONES digit.