Answer: Choice A
Ahmed started 6 floors above ground level, then he went down 8 floors
The +6 or simply 6, is positive, so he's on the 6th floor to start. Then adding on -8, which is the same as subtracting 8, moves him down 8 floors.
6 + (-8) = 6 - 8 = -2 indicates he's 2 floors below ground level, so he's in basement level 2 (perhaps some kind of parking garage).