The Ideal Mechanical Advantage (IMA) of a lever is the ratio between the length of the effort arm and the length of the resistance (load) arm:
[tex]IMA=\frac{L_e}{L_r}=\frac{50}{5}=10[/tex]
Correct answer c) 10
Notice that I've transformed the effort arm from 0.5 meters in 50 cm, to match the unit with the resistance arm.