Explanation

(a) Temperatures $T_{1} = 15℃ = 15 + 273 = 288$ K
$T_{2} = 35℃ = 35 + 273 = 308$ K
Volume remains constant.
So, $\frac{p_{1}}{T_{1}} = \frac{p_{2}}{T_{2}}$
$\frac{p_{1}}{p_{2}} = \frac{T_{1}}{T_{2}}\ \ \ \ \ \Rightarrow \frac{p_{1}}{p_{2}} = \frac{288}{308}$
$\frac{p_{2}}{p_{1}} = \frac{308}{288}$
% increases in pressure=$\frac{p_{2} - p_{1}}{p_{1}} \times 100$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{308 - 288}{288} \times 100 \approx 7\%$