Which of the given values of \( a \) makes the statement true?
\[ a\cdot\int\limits_0^{\frac{\pi}2}\cos x\,\mathrm{d}x=\int\limits_{2\pi}^{3\pi}\sin x\,\mathrm{d}x \]
How many times bigger is \( \int\limits_0^7\left(-\frac47x+4\right)\,\mathrm{d}x \) than \( \int\limits_{-1}^0\left(-\frac43x+\frac43\right)\,\mathrm{d}x \)?