Data Presentation Problem Solving

$\begin{array}{|c|c|c|c|c|} \hline & \text{High School} & \text{Middle School} & \text{ Total}\\ \hline \text{Boys} & a & 2b & X\\ \hline \text{Girls} & 2a & b & Y\\ \hline \text{Total} & M & N & T\\ \hline \end{array}$

In the table above, each letter represents the number of students in that category. Which of the following equals $M-N?$

(A) $\ \ X$

(B) $\ \ Y$

(C) $\ \ 3(Y-X)$

(D) $\ \ \frac{T}{3}$

(E) $\ \ X+Y$

The graph above shows the cost of manufacturing of two products, A and B, per year. In which year was the difference in the cost of manufacturing the two products the greatest?

(A) $\ \ 2001$
(B) $\ \ 2002$
(C) $\ \ 2003$
(D) $\ \ 2007$
(E) $\ \ 2008$

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The above chart shows the temperatures in a city over several days. What is the sum of the median and mode of the eleven temperatures?