@audrey One more thing...

"Notice that since a, b, c, and d are all less than or equal to five, the sum of each column will be **less than 10**. Then we can look at the digits of 14762 and directly see which of a, b, c and d were added together to get it. "

Should be:

Notice that since a, b, c, and d are all less than or equal to five, the sum of each column will be **less than or equal to 10**. Then we can look at the digits of 14762 and directly see which of a, b, c and d were added together to get it.