To figure out who "J" and "SL" are, think about which characters have those initials in their names.

To figure out who "L" is, look at the letter's handwriting and compare it to other sources of handwriting.

There is only one character whose name starts with "J" — Jessica — and the letter was found inside Jessica's bag. "J" is Jessica.

There is only one characters whose initials are "SL" — Summer Lachance. "SL" is Summer.

There are two characters whose names start with "L" (Luna and Luka). If we compare their handwriting (we can look at Luna's witness statement and the letter Luka wrote to Dante) to the letter's handwriting (the letter found in the gray bag), we can tell the letter was written by Luka. "L" is Luka.

Now we know that Luka wrote the letter to Jessica, telling her that if she (Jessica) can't pay by Friday, she needs to leave something ("it") in Summer's office. What is "it"?

To figure out what "it" is, read Summer's blog posts, keeping in mind when the letter was written (August 19th, 2019) and the deadline mentioned in the letter.

The letter is written August 19th, 2019. The letter says that if Jessica can't pay by Friday, she needs to leave something in Summer's office. Friday would be August 23rd, 2019. Did Summer post any blog posts shortly after August 23rd, 2019, indicating that she found something in her office?

Whose fingerprints were found on the blue envelope?

The letter was written on August 19th, 2019, a Monday. The letter says that Jessica needs to leave something in Summer's office if she (Jessica) can't pay by Friday. Friday would be August 23rd, 2019.

On August 26th, 2019, Summer found a blue envelope in her office (see the blog post titled "Surprise). There are two sets of fingerprints on the envelope: Summer's and Jessica's. We can assume Summer's fingerprints are on the envelope because she found it and handled it. We can infer that Jessica left the envelope in Summer's office over the weekend (or late on Friday/early on Monday) because she failed to pay Luka by Friday (August 23rd). This explains why Jessica's fingerprints were found on the envelope.

The answers to this task are:

• "J" is Jessica
• "SL" is Summer
• "L" is Luka
• "It" refers the envelope Jessica left in Summer's office (the answer is "envelope")