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Given that \(\displaystyle\int_{1}^{3} f(x)\,\mathrm d x = 4\) and \(\displaystyle\int_{1}^{3} g(x)\,\mathrm d x = -2\), find:
\(\displaystyle\int_{1}^{3} (f(x) + g(x))\,\mathrm d x=\)

\(\displaystyle\int_{1}^{3} (2f(x) - 3g(x))\,\mathrm d x=\)