knowing the places of where the number is the value of what the digit is whether it be in the millions, thousands, or ones places...
The ones column are in single digits and if there are none then the 0 digit is used.
That means multiply it by 2. If your tens digit is 3, your ones digit is 6.
Six places to the left of the units digit is the millions digit.
22621, 44742, 66863, 88984
91 since the ones digit is 8 less than 9 and the two digits, 9+1 = 10, a two-digit number.
There is a lot of answer for this, but I tell you one. The answer is 6541.