Answer: 69.8 degree
Step-by-step explanation:
F*cos(theta)
is your pushing force projected along the x axis and
-F*0.368*sin(theta)
is the friction force generated by the pressure downwards
when F cos(theta) = F*0.368*sin(theta)
the box wont move no matter how large F is, because you are adding no net force along the x-axis
so sin(theta)/cos(theta) = 1/0.368
tan^-1(1/0.368) = theta
theta = 69.8 degrees