I am still not sure what you meant by "time interval is 10m/sec". If I am correct, it is a typing error. That should be 10msec (milli second).
10^6 bits in 1 sec
therefore bits that can be transferred before the timeout is = 10^6 * 10/1000 = 10000 bits
and avg msg size is (0+1000)/2=500 bits
number of frames (or msgs) that can be transferred are 10000/500=20
D) NONE