Squaring a 2-digit ending in 3

Steps
take a 2-digit number ending in 3.
the last digit will be ___9.
multiply the first digit by 6: the second number will be the next to the last digit: __X9.
square the first digit and add the number carried from the previous step: XX__.

Example
if the number is 43, the last digit
is ___9.
6 x 4 = 24: __49.
4 x 4 = 16, 16 + 2 = 18 (add carry): 1849.
so 43 x 43 = 1849