Question 626369
Hint: "the difference of two numbers is 12" means {{{x-y=12}}} where x is assumed to be the larger number.


"the larger number is one less than twice the smaller number" means {{{x=2y-1}}}


So start with {{{x-y=12}}} and replace x with 2y-1 to get {{{2y-1-y=12}}}