Question

The missing expressions and output values on Jenna's table

Answer 1

Jenna writes 5 fewer facts than Cleo.  Let "c" = number of facts Cleo writes.
So an expression we can use to figure out how many facts Jenna writes is:

c - 5

So the table could look something like this:
10 ║ c-5 ║ 5
11  ║ c-5 ║ 6
12 ║ c-5 ║ 7

So if Cleo writes 31 facts, we can still use: c - 5 
Plug in c = 31 to get:
31 - 5 = 26 facts for Jenna