The graph as a whole is informing us how the word "you" became more used compared with that of "ye" for 3 regions in England.
The first question asks: "The area of early modern England that was first to favor the use of you over ye was ?"
What this question is asking is: which of the 3 regions (London, North, East Anglia) was the first to use "you" more often then "ye". This means that "you" is happening more than 50 percent of the time. If we were to draw a horizontal line with it's value equal to 50% the first population to cross this threshold would be London.
Second question: This question is only concerned with the area of the north, we can ignore the other two lines on the graph. It also only only cares about the time from 1520-1559. This is a mark on our x-axis. When we draw a vertical line on 1520-1559 we know that we cross the "North" line
20 percent.
Hope it helps.