It's a little hard to tell what is supposed to go in the middle column. The column on the right can be filled directly from the problem description: at 2 calendar years, the equivalent is 24 human years, and the number of human years increases by 4 for each increase of 1 calendar year.
The multiplier in the expression is obviously 4, as we are told the number of human years is 4 times the difference from 2 calendar years. (each year after 2 ...)