Based on shearing of rivets:
$P = \tau A$
$P = 14 [ \, 4 (\frac{1}{4} \pi) (\frac{3}{4})^2 \, ]$
$P = 24.74 \, \text{kips}$
Based on bearing of plates:
$P = \sigma_b A_b$
$P = 18 [ \, 4 (\frac{3}{4})(\frac{7}{8}) \, ]$
$P = 47.25 \, \text{kips}$
Safe load P,
$P = 24.74 \, \text{kips}$ answer