As we know that 10-bAse data travels at the rate of 10 mbps, therefore at 1 sec we have 10240 bytes. 
 We have to calculate for 64 bytes travelling in one second. Multiply both sides by 64. 
 64 sec = 10240 x 64 bytes 
 64 bytes = 64 / 10240 sec
 Now we have to calculate for light of speed 
 1 sec = 186000 miles 
 Substitute this value to the formula above 
 64 bytes = 64 / 10240 x 1 sec = 64 / 10240 x 186000 miles = 64 / 10240 x 186000 x 5280 feet = 6138x10^3 feet 
 Therefore, 64 bytes is equal to 6138 x 10^3 feet long message