Concept: The question tests on the basics of equations in the format of a Word Problem in DS
Let the price of each donut be a$ and that of a bagel be b$.
St (1) 10a + 6b = 12.90
- 5a + 3b = 12.90 /2
St (2) Given a = b – 0.15
Thus 5a + 3b
= 5(b-0.15) + 3b
We do not know the value of a or b and hence Insufficient.
Thus option (A)