= 5200 + 2xy


\[ 37p + 7q + r = 45 \quad \text{(E3)} \]
\[ (19p + 5q + r) - (7p + 3q + r) = 25 - 11 \]
\[ 12p + 2q = 14 \]
\[ 6p + q = 7 \quad \text{(E4)} \]
\[ (37p + 7q + r) - (19p + 5q + r) = 45 - 25 \]
\[ 18p + 2q = 20 \]
\[ 9p + q = 10 \quad \text{(E5)} \]
\[ (9p + q) - (6p + q) = 10 - 7 \]
\[ 3p = 3 \Rightarrow p = 1 \]
\[ 6(1) + q = 7 \Rightarrow q = 1 \]