Suppose $Z$ is the distance between the breaking point and one end point of your rod. Then Z~U(0,1)
So P(The longer piece has length at least 0.6 meter)=
$P(Z>0.6$ or $Z<0.4)=P(Z>0.6)+P(Z<0.4)=(1-0.6)+(0.4)=0.8$, that's the answer of you question.
Notice that you cannot use two dimension plot to help you solve this problem because X and Y are correlated, there is no way to solve it by this kind of plot.
5ii:
You should first show that in order to prove 5ii, you need to prove:
$P(AB)+P(BC)-P(AC)
Hint:using 5i to expand every item.
Then you should know $P(A\cup B)=P(A)+P(B)-P(AB)$
Try to expand $P\\{(AB)\cup (BC)\\}$ and prove $P(AB)+P(BC)-P(AC)