Problem 513 | Friction

$N = 300 \cos \theta = 300(\frac{4}{5})$

$N = 240 \, \text{ kg}$
 

$f = \mu N = 0.45(240)$

$f = 108 \, \text{ kg}$
 

$\Sigma F_x = 0$

$P + f = 300 \sin \theta$

$P + 108 = 300(\frac{3}{5})$

$P = 72 \, \text{ kg}$           answer