Walter arfeuille of belgium lifted a 281.5 kg load off the ground using his teeth. suppose arfeuille can hold just three times that mass on a 30.0° slope using the same force. what is the coefficient of static friction between the load and the slope?

Gravitational, g = 9.81 m/s2 
Theta = 30 degrees, using the same force. 
Let u be the coefficient of static friction 
Force applied F = mg 
Static Friction Force = u3mgcos (theta) 
The gravitational Force = 3mgsin (theta) 
So the force equation = 3mgsin (theta) - (u3mgcos (theta) + mg) = 0 
So 3mgsin (theta) = (u3mgcos (theta) + mg) => 3sin (theta) = (u3cos (theta) + 1)
 => u = (3sin (30) - 1) / 3cos (30) => u = (3(1/2) - 1) / (3 x 0.866)
 => u = (1.5 - 1) / 2.59 = 0.5 / 2.59 = 0.5 / 2.598
 Coefficient of Static Friction u = 0.19.