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*