C@RL is to 36Y? in the same way as H2$$\uparrow$$C is to---

C@RL $$\Leftrightarrow$$ 36Y?

If we, look at the pattern, C is 7th from left end while 3 is 7th from right end.

@ is immediate left of C while 6 is immediate right of 3.

R is immediate right of C while Y is immediate left of 3.

L is second to the left of C while '?' is second to the right of 3

The pattern is : what's happening to the first word, the opposite of it is applied to the second word.

Now, for H2$$\uparrow$$C, following the same pattern, we get :

H is 13th from left end, so 13th from right end = J

2 is second to the left of H, so second to the right of J = 4

$$\uparrow$$ is third to the left of H, so third to the right of J = +

C is sixth to the left of H, so 6th to the right of J = 3

$$\therefore$$ H2$$\uparrow$$C $$\Leftrightarrow$$ J4+3