To find the probability that Eli will get a black pen and not get a green highlighter, we first need to find the total number of possible outcomes.
There are a total of 7 black pens and 5 blue pens in his desk drawer, which means there are 7 + 5 = 12 possible pens he could choose from.
There are a total of 3 yellow highlighters, 2 green highlighters, and 5 pink highlighters in his pencil case, which means there are 3 + 2 + 5 = 10 possible highlighters he could choose from.
Therefore, the total number of possible outcomes is 12 (pens) x 10 (highlighters) = 120.
The number of favorable outcomes (getting a black pen and not getting a green highlighter) is 7 (black pens) x 8 (highlighters that are not green) = 56.
So, the probability that Eli will get a black pen and not get a green highlighter is 56 (favorable outcomes) / 120 (total outcomes) = 7/15.
Therefore, the correct answer is 7/15.