If you have the data in fasta format in your history already, skip
converting to fasta-> tabular and just use that with the tool
"FASTA manipulation -> Compute sequence length". Then run the
statistics tool on the output.
Or, if this is the format you have to start with (tabular), the tool
"Text Manipulation -> Compute" can be used with the option
"length(c2)" to generate the length of column 2. Adjust the "c2"
portion as needed if this is not your complete file or if you had to
do extra manipulations to isolate these columns (potentially skip
those steps and use the earlier file).