By Green's theorem, we have
[tex]\displaystyle\int_C\left(7x+\cos\frac1y\right)\,\mathrm dy-(3y^2+\ln(3x))\,\mathrm dx[/tex]
[tex]=\displaystyle\iint_{[1,4]\times[0,3]}\frac{\partial\left(7x+\cos\frac1y\right)}{\partial x}-\frac{\partial(-(3y^2+\ln(3x))}{\partial y}\,\mathrm dx\,\mathrm dy[/tex]
[tex]=\displaystyle\int_0^3\int_1^47+6y\,\mathrm dx\,\mathrm dy=\boxed{144}[/tex]