The larger of two numbers is five more than six times the smaller number. The sum of the numbers is fifty-four

The two numbers are 9 and 45. It's mostly just educated guessing - you start with a random number like 10 and multiply that by 5 which is fifty. 10+50 = 60 which is too big. Because it's too big, but still close to the number you want you go down one number. Nine. Nine times five is 45. 45 + 9 = 54