Confidence interval, in statistics can be defined as the probability that a population parameter will fall between two set values( upper and lower bound) for a certain proportion of times. Therefore, there's 99% chance that the true difference in RDI levels between men and women is contained within the 99% Confidence interval shown in the previous questions.
The graph (although it doesn't show it) is making points at every 20 (dollars) mark and also lines up to each hour mark, meaning that for every hour, Tanya makes 20 dollars.