The solution shows '@[fares;where null fares;:;avg fares]', but to actually amend the list, it should be @[`fares;where null fares;:;avg fares], right? The backtick is needed to amend the fares list.
I should have been more clear in my post. The solution in the exercise is wrong. It mentions amending the table, but their solution doesn't include the backtick.
In Session 3 Data Structures, Exercise 17 it says "Amend the fares list to replace the null values to be equal to the average value". The solution it shows is "@[fares;where null fares;:;avg fares]". This is incorrect. It's missing the tick prior to "fares".