Concept: The question tests on the application of exponents and equation in a DS format.
Solution:
2x+y = (22)8 = 216
x +y = 16
St (1) x2 = 81 and thus x = 9, - 9
Hence y = 7, 25
No unique value of y is obtained. Insufficient
St (2) x-y =2
Along with x + y =16 (given) a unique value of y = 7 can be obtained.
Thus Sufficient.
Hence option (b)