motion and rates

For part (iv) of this question, I understand the shape of the displacement-time graph in the solution, but how do you use the graph given in the question to find that the displacement at 4 and 6 seconds is 6m, as well as the displacement being 8m at five seconds?

can someone please help me with b. is there a way to find i0 that i missed?. How can i get L without finding io. even if i find io im a bit lost :(. if anyone ends up doing this thank you and i love you