def Length(screw, W_req, W, extra):
    L = W_req/W + extra
    print('#{} Screws need a minimum length of {:.2f}"'.format(screw,L))

screws = [(6,69),
          (7,76),
          (8,82),
          (9,89),
          (10,95),
          (12,108)]

for screw, W in screws:
    Length(screw,80,W,5/8)

from numpy import arctan, degrees, cos, sin, sqrt
alpha = arctan(80/40)
print("Angle = {:.2f} degrees".format(degrees(alpha)))

Z_a = (82*1.375*52.8)/(82*1.375*cos(alpha)**2 + 52.8*sin(alpha)**2)
print("The combined load resistance Z_a = {:.2f} lb".format(Z_a))

print("The required Z_a = {:.2f} lb".format(sqrt(80**2+40**2)))