(a)
From van der Waals’ equation,
$\left( p + \frac{n^{2}a}{V^{2}} \right)\ (V - nb) = RT$
$\left( p + \frac{2.253}{0.25 \times 0.25} \right)(0.25 - 0.0428)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 0.0821 \times 300$
$\ (p + 36.048)(0.2072) = 24.63$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ p + 36.048 = 118.87\$
$p = 118.87 - 36.048 = 82.82\ atm$