Ans. B

Now there may be various method to solve it but if we consider basic methods such as 

1. Mesh analysis.
2. Node analysis.

Consider mesh analysis above circuit consist of Supermesh (current source common between common branch e.g. 2A current source in above ckt.) so number of equation required will be 2(one for super mesh and other for loop without super mesh )

but if we consider node analysis only single equation suffice need, so using node analysis we get

At node X,

I1 +  2 = I2

4 - 3 Vab  - Vab  = -20

Vab = 6