TCP congestion control example

Consider the figure below, where a TCP sender sends $8$ TCP segments at t$=1,2,3,4,5,6,7,8.$Suppose the initial value of the sequence number is $0$ and every segment sent to the receiver eachcontains $100$ bytes. The delay between the sender and receiver is $5$ time units, and so the first segmentarrives at the receiver at t $=6.$ The ACKs sent by the receiver at t $=6,7,8,10,11,12$ are shown. TheTCP segments $($if any$)$ sent by the sender at t $=11,13,15,16,17,18$ are not shown.The segment sent at t$-4$ is lost, as is thACK segment sent at t$-7.$

a$)$ What is the sender action at t $=11$ upon receipt of the ACK?b$)$ What is the sender action at t $=13$ upon receipt of the ACK?

c$)$ What does the sender do at t$-16?$ You can assume for this question that no timeouts haveoccurred.

d$)$What does the sender do at t$-17?$ You can assume for this question that no timeouts haveoccurred.

e$)$ Suppose that the next event after t$-17$ is a timeout event. What does the sender do$?$