You Said:

C. First he experimented, then proposed, and lastly rearranged to get his answer.

Right! Here’s the process the student told me he followed to get the answer:

First, he experimented to find what number when multiplied by itself would result in the digit one in the one’s place of the product. That number was the number “9.” The value of the letter “Z” was 9.

Second, he proposed that he could discover the identity of the letters in the multiplicand by dividing the multiplier into product. Why did he think this way? Because he knew you could check a division problem by multiplying the quotient by the divisor and get the dividend (if he divided correctly in the first place). He thought the opposite process would work, and it did!

Third, he rearranged the problem and divided. In other words, he divided 9 into 111,111,111. When he did, he found that the letters represented the following numbers:

    S= 1     T= 2     U= 3     V= 4     W= 5     X= 6     Y= 7      Z= 9

Just to be sure he was right, he worked the problem again, substituting the numbers for the letters and he got the answer, 111,111,111.

Like Edison who said, “Genius is 1% inspiration, and 99% perspiration,” his bias for experimenting and perseverance paid off!