In Part A you chose an expression for the pattern that the numbers continue in. Part B is asking you to use that expression to find the 20th number in the pattern.
If the expression is 4n+4 and n represents the #th number then this is how you would solve the expression:
The 20th expression would be 80. Counted on my fingers xD hit 80 when i did 20 fingers. which means that if you put 20 as n, it should come out to 80, but it comes out to 84 by the answer you chose, so I'm wondering if the answer you chose was right, or if it was A