Here, 4 digited numbers means the number of binary digits are 4.
Since B >= A, it means we have to count all cases for every possible value of A.
If A = 0000 , B can take values from 0000 to 1111 i.e. 16 values.
A = 0001, B can take 0001 to 1111 i.e. 15 values.
Similarly, it will take 14 , 13 , 12 , 11 , .... 1(when A = 1111 , B can take only 1111).
So, total number of values are 1+2+3+...+16 = 16(16+1)/2 = 136.
So, Option B.