The graph shows price decreases with age, so the minimum price will be associated with cars that are 3 years old. We read from the graph that the price of a 3-year-old car is about $11,600. (This is slightly more than halfway between the $11,000 and $12,000 grid lines.)
The maximum will be associated with a 2-year-old car. We can read the graph to find the price of a 2-year-old car is $14,000. That value is on the grid line, so no guessing is necessary.
Then we have ...
We'd like to check our guess of the minimum using the given price equation. Filling in x=3 in the equation, we get ...
2400·3 +6800 = 7200 +6800 = 14,000 . . . . matches the maximum, not the minimum
We observe that the equation has a positive coefficient for x, so will be the equation of a rising line, not the falling one shown on the graph.
For "fun", we can check to see what the equation gives for x=2:
2400·2 +6800 = 4800 +6800 = 11,600 . . . . matches the minimum, not the maximum
This gives us some confidence that our choice of numbers is correct, but makes it clear that the equation is incorrectly written.
The problem needs to be reported, so it can be fixed.
You already got the first two questions right: the group with the highest number of people unemployed / unemployment rate is the one with the highest bar in the respective histogram.
The two graph are related in this sense: take the first age group as reference. We know that 700 people from 16 to 19 are unemployed, and that those people represent 14% of the population, then we know that the 14% of the population between 16 and 19 is 700.
We can deduce that, if x is the number of people between 16 and 19, we have
So, by the relation between the two graphs, we can deduce the total population for each age group.