sender transmit bits from sequence number 62-66.
Rn=64.receiver window is currently at seq no 64.and acknowledgment is 65 it means data is reached until bit no 64.(it is cumulative ack).
seq no of pending data packets are 65and 66.
pending ack are 66 and 67.(if sender receive these ack's it means bits 65 and 66 are reached safely so entire packet is reached safely)