The correct answer is œoption 4.CONCEPT:Bandwidth: It is the speed of bit transmission in a channel or link per second.It is the number of bits per second that a channel, link, or network can transmit.Transmission time: It is the time between the first bit leaving the sender and the last bit arriving at the receiver.It can be calculated as :Transmission time = Message size ÷ BandwidthPropagation time: The time required by the bit to travel from source to destination is called propagation time.It can be calculated as :Propagation time = Distance ÷ propagation speedRound Trip Time(RTT): It is a time to travel from source to destination and again come back to the source.It is twice of propagation time.CALCULATION:RTT: 500 millisecondMessage size: 1000 bitsBandwidth : 50kbpsRTT = 2 x Propagation time 1. Propagation time = RTT / 2= \(\dfrac{500 \rm \ ms}{2}\) = 250 ms2. Transmission time = \(\rm \dfrac{1000 \;bits}{50 \;kbps}\)= \(\dfrac{1000}{50\times1000\times10^{-3}}\)ms= 20 msThe total time for the receiver to receive the frame= Propagation time + transmission time= 250ms + 20ms= 270msHence, the correct answer is œoption 4.