Question

the unit digitsof a two numberis 1 less than twice the ten digit. if the sum of tje digits is 9, find the number.

Answer 1

Are you sure this is written correctly? Any number whose digits add to 9 is divisible by 9.  For a 2 digit number then, your choices are
18, 27, 36, 45, 54, 63, 72, and 81.  None of these has the property that for the 2 digit number AB that B=2A-1.  Solving your question algebraically is possible but you get fractional digits.