The number of non-empty subsets of the set $\{1,2,3,4\}$ is 3 x a. The value of 'a' is

Total number of subset of given set $\{1,2,3,4\}=2^4=16$

Since,$\varphi$ is the subset of every set.

$\therefore$ Number of non-empty subsets $= 16 - 1 = 15 = 3 x 5$