V=πr^2 h
Volume= pi • radius squared • height

Square 12.1, and subtract 121 from both sides.

Complete the subtraction on the right side.

This is the solution.
Here's the answer to your questions
How I understand from your writing next term is equal previous plus 3,
if 1st is -4, then next (second) should be -4+3= -1
The answer is A,because the way your question is written,there would be 4 molecules of salt (NA) and one molecule of CL (Chlorine)