Resolve force P into components at its x-intercept
$M_B = 40$
$2P_y = 40$
$P_y = 20 \, \text{ lb}$
$M_A = 170$
$3P_x + 4P_y = 170$
$3P_x + 4(20) = 170$
$P_x = 30 \, \text{ lb}$
Resolve force P into components at its y-intercept
$M_A = 170$
$(3 + b)P_x = 170$
$(3 + b)(30) = 170$
$b = \frac{8}{3}$
Thus, y intercept of force P is (0, -8/3). answer