If NOR is coded as 2-3-6, then how should REST be coded in the same code language ?

Difference between alphabetical positions of N and O = 1 = difference between 2 and 3 Difference between alphabetical positions of 0 and R = 3 = Diff. between 3 and 6. 

Similarly, for REST, 

difference between Rand E = 13,

 difference between E and S = 14 and 

difference between Sand T = I 

Here, only option ( c) follows above condition