x + y = 9 equation 1<span> the sum of the digits of a two-digit number is 9
</span>the number formed by interchanging the digits is 27 less than the original number<span> we are looking at the number xy, 10x+y for x is a tens digit. 10y + x = 10x + y + 27 simplify it, 9y = 9x + 27 divide by 9
</span>x + y = 9 equation 1 y= x + 3 equation 2 by subtitution we put y in equation 1
