Given,Bandwith of Network=10Mbps.
So,Number of packets can be transmitted through network per second=10Mbps/10000bits=1000 packets.
Since Network utilization is .75 so efficient number of packets that can be transmitted through network per second=.75*1000=750 packets.
Now talking about each nodes.
Average rate of each of each node=1Mbps.
So,number of packets sent by each node in 1 sec=1Mbps/10000bits=100packets.
Total number of packets sent by all 8 node combined=800 packets.
Therefore, Fraction of collision = (800-750)/800=50/800=6.25%