Step 1: {Identify the distinct letters}
The word 'MONOTONE' has the following distinct letters: M, O, N, T, E.
Step 2: {Count the distinct letters}
There are 5 distinct letters.
Step 3: {Use the formula for the number of subsets}
The number of subsets of a set with \( n \) elements is \( 2^n \). In this case, \( n = 5 \).
Step 4: {Calculate the number of subsets}
Number of subsets = \( 2^5 = 32 \).
Step 4: Conclusion
Therefore, the number of subsets of the set of letters in the word "MONOTONE" is 32.
The correct answer is: 32