A three- digit number between 600 and 700 is one less than 30 times ths sum of the digits. If the tens digits is one less than the units digit, What is the number?

Answer 1

unit digit --- x
tens digit --- x-1
hundred digit --- 6 , to be between 600 and 700

Just translate the English into Math using my definitions:
the sum of the digits = x + x-1 + 6
the 3-digit number = 600+10(x-1) + x
600 + 10(x-1) + x = 30(x + x-1 + 6) - 1

solve for x and all mysteries shall be revealed.

Answer 2

x+x-1+6