Rtt is 2 x 270=540 ms. ( You can calculate yourself)
The RTT here in not of ACK but the time by which you, the sending station would get the signal from your frame , if your frame got crashed right before me, the receiver station , that is the maximum time after which you can be sure that your frame is safely with me.
Transmission time is : 1ms ( You can clearly calculate)
Hence you could have transmitted 540 frames in this time.
But you have a 3 bit sequence number, meaning at most 7 frames, one of which is already the one sent.
So, basically you are sending 6 frames in the time you are supposed to send 540 ones .
Therefore throughput : 6/540 x 1 Mbps = 11.377 Kbps.